The powers received from Hagoromo may very well be temporary or permanent. I lean toward temporary, as you know. One, having too much power invites conceit. These are words Hagoromo said to what happened to his mother.
While I'm not trying to say Naruto of all people will get arrogant, it's better just to not have that kind of temptation constantly. Second, the powers are limited to their respective right and left hands. We've seen whenever they use the sages power, they use the hand that has the marks of their representative moon on their hand. Sasuke, who by no means should have inherent sage chakra, is able to generate the Black Chidori through his left hand. There's a reason why the Sage said to put their dominant hands on his staff, because it's the hand they most commonly use.
He's the pot calling the kettle black. Hagoromo was gifted with powers inconceivable to the modern man and besides having a high opinion of himself he handled things like someone who had the strength of character to not allow his power to corrupt him. Every person handles authority differently. Many are able to maintain some self-restraint and not let their strength go to their heads. True, you do have a few bad apples who take what they have to the extreme, but that in no way should be used as a justification to impose some blanket standard of possession when it is only a few, not the many, that are pushing the ethical boundaries with their power. You don't see any of the Alliance forces or the Kages pushing for hegemony over the rest because they might have a few more weapons and men than the foreign national standing next to them. It's mostly the figureheads of the Uchiha (whose adopted ideology could be simplified to "might makes right") and those who think like them that have been the cause for most of the dangers being faced now.
Accusations of corruption should be saved for those who have actually let their power override their judgement. I don't know about Sasuke, but Naruto already had this possibility brought to his attention by Itachi back when the main war was ongoing, he's aware of the risks that his power brings. If he ever chooses to drop his morality lessons for a high and mighty attitude then the alarm can be raised. But for the time being, I don't think we should be so quick to strip Naruto down to nothing for the actions of other people. Besides, when Hagoromo made that statement, it was mostly directed towards Kaguya - the woman who is literally absorbing the chakra of people from around the world. That would be a textbook example of a person mishandling their authority and power. If anyone should be judged, it's her.
I'd imagine it would be awkward invoking these powers through their other arms, and crippling their efficiency.
Crippling their efficiency? They're not trying to look two ways at once. These markings merely act as ducts for the chakra they were given. It's hardly any different than the air tubes that Zaku carved through his arms to release his specialized jutsu. These aren't Genin who have just gotten out of the academy who have no idea about the chakra pathway system. They've demonstrated a level of control over their chakra that's nothing less but amazing. Giving them the means to channel the Sage's chakra through their other palms would in no way be hazardous to them unless there's a limit of only one appendage to use these powers with that I'm missing.
Third, the manga is consistent when issuing a power balance. Not one person or village would have too much power. Having Sasuke and Naruto keep these powers will destroy that balance, completely.
What power balance? This idea of a restrictive ceiling preventing other nations from being able to have an equal say in things is just hogwash. No sooner could these powers be removed that you would have to empty their genetic makeup of the components that make them more naturally gifted than others or enact policies of societal/economic/military downsizing in the largest villages because they happen to have a larger population or more clans living in their borders.
Again, if people allow paranoia to run their lives then the Narutoverse is no closer to achieving peace than the era when wars were being waged one after the other.
The Bijuus I still see no reason to they have to stay inside Naruto. Previous build-up, hints that they will be free and live in their own way. Plus, we have to consider the actual Bijuu are not inside Naruto, but Kaguya. What naruto has is a piece of their real form, and what will happen to those pieces once the Bijuu are free again? What will happen to Kurama with him being split into two entities? Will the other half remain seperate, or will they both merge either outside, or inside Naruto? This leads me to believe that whatever happens will be circumstantial that leads to one conclusion. We know both halves will have to join together again, but how and where will they inevitably reside afterwards. It's not just about Naruto and his supposed destiny. We have to think of Gaara and Bee as well, who are the only ones left alive to continue bonding with the Bijuu they held within them.
Hagoromo's main interest with the bijuu was for them to not be looked at and exploited as creatures of destruction. The planted seeds of mistrust and resentment are what compelled them to turn their backs on those ambitions and carry out their personal sprees of terror. Now that they've finally received the recognition they were so desperately crying out for, they're willing to cooperate with humans. Does that mean that they're going to allow themselves to be extracted from Naruto at the expense of his life? I would hope not, but how they handle their newfound roles in the shinobi world is a mystery. The idea of them wanting to live independently seems like it'd be the next logical step to take after being released from the shackles of servitude. But the truth is that there's been no statement made (that I know of) from any pacified bijuu expressing the wish to leave their human companions. We had some of the more embittered bijuu trying to break free so they could continue killing, but the bijuu now have shown no such enthusiasm. Does this mean that they no longer have the desire to live independently? Maybe, maybe not... I can only go by the docile nature Gyuki showed in his close friendship with Bee and the statements made by others that allude to the idea that the bijuu would be willing to continue living inside of Naruto until at least the end of the manga (eventually overtaking the previous Hokages strictly in the technical sense which I doubt Kishi would recant, Naruto's persistent desire to become stronger, and Hagoromo's prophetic remarks about the bijuu coming together to know true power).
Nearly all of the jinchuuriki have died. However Gaara and Bee will react to Shukaku and Gyuki being in separate bodies is unknown, but their opinions aren't the main issue. Naruto is still a vessel for bits of the nine creatures' chakra. Even after this battle is over, besides everything that's been said, he'll still have use for their abilities, especially if he intends to fight Sasuke with the power ups he's gotten.
Sakura and Kakashi have just as much stake in this fight as Naruto and Sasuke, simply because they are here. If they didn't have any stake, they would have been put in IT along with the rest of the world. Sakura from the latest chapters is hinted to have something happen to her, at the least. She wants to stand with the boys.
Kishi certainly gives them more privilege than any of the other Rookies. This makes me think back to the climactic reunion Team 7 had during the Kage Summit. After everyone who wasn't of any importance to the group had been conveniently knocked out, they had their conversation which set the wheels in motion for Sasuke to develop EMS, meet Itachi, and ultimately have a heel-face turn. Most of the important interactions were made between Sasuke and Naruto, because the plot is chiefly focused on them. They're carrying most of the weight but the others do have their uses, their relevant points. Kakashi's was during the Black Zetsu fight and Sakura has been in the limelight on a few occasions now. I doubt we've seen the last of them but it's unlikely that they'll be the ones going toe-to-toe with the antagonist (assuming Kishi's usual standards hold up in this fight).
We wouldn't be seeing her get depressed and insecure of not matching them if that wasn't what she wanted. It will just be a poor cop-out to not have her succeed in her goal, and resign herself to always be relegated to the back.
There's no mistake that Sakura was put here for a reason, but I don't believe that it's going to result in this breathtaking reversal of fortune that'll skyrocket her status to legendary with a golden statue made that's as big as Naruto and Sasuke's. If she takes the initiative again, I think it'll be brief, but it won't come without causing a change that influences the course of things in some way.
With Kakashi, we still have Obito around. We don't know what Madara did to him, while transferring their eyes., but Kakashi will want to save his friend, if given a chance. Hamura is just one possibility.
His friend is likely to die whether he wants it to happen or not. If the extraction process doesn't kill Obito then something else will. Like others have said, having him removed now prevents any of the hassle that would come with holding him responsible for the multitude of heinous crimes he's committed. I think Kakashi and Naruto will have enough decency to keep his body in-tact though.
The main point is that they get something to be able to participate, that's not by fighting fodders. What would be the point to keep them here, if it was just that. I just don't see the reason why Kishimoto would have them here for something that seems so minor compared to fighting Kaguya. Plus, it's under the assumption the transformed White Zetsu will be able to turn back to normal, but having it stated right away, and act as time limit goes against that speculation. From Black Zetsu and Kaguya's words, the transformation to White Zetsu will take time. That's why Kaguya transported Team 7 and Obito to another place, away from her nursery, so they don't damage it in anyway that could hinder the process. Right now, Kaguya is in front of them, and she won't have them go near the tree. In order to save everyone, they have to take her down. It's the only option available to them.
This battle has more participants than just Kaguya for the Akatsuki's side. It's not like Spiral Zetsu is a fragile grunt who can't survive for two minutes when going into a fight. He was keeping the entire Alliance on their toes for quite awhile. If he's at least as strong as Black Zetsu, Sakura and Kakashi have someone to fight that's fairly powerful in his own right. And I doubt Spiral Zetsu decided to just take a break and frolic in the carnage. He's the only friend Kaguya has left, her only lieutenant. Surely he would come to his maker's aid. Even if the White Zetsu army doesn't turn up, Spiral Zetsu is the next best thing. His presence allows Team 7 to finish off the last sympathizer to Kaguya's cause while Naruto and Sasuke play out the Sage's grand escapade he had with his brother and the Jubi.