I think the fact that there's no real romance implication from the second player, as in the person who's being questioned to love the first, harms the whole romance in general. NS got that cover. In NH, as I said before, in 615, Naruto is the second player because he's being questioned by fans if he is getting feelings for Hinata. Sadly, there is no indication. It goes the same with Sasuke. Now you said that there's little for NS. Here's the thing: they're coming from Sakura, the second player in NS.
Naruto is first player because we know he loves her, so anything he does something about love is no surprising. However, when the other player does it, it is because she's being in position of "what do you see in first player, Naruto?" Take the feeding scene for example. Noticed that it started off as a serious moment, no comedy whatsoever. When Sakura was going to feed him, Naruto looks very genuine and there's no comedy face like hearts or anything because this moment was true romance implication. It became comedy when Sai messed up and noticed it happened in the next page, meaning a fan would get so hype to turn the page, only to face palm and say, "So close!" That's the beauty of manga, hype before next page is turned.
I can go on, but hopefully you understand what I mean.

Well ever since part 2 started, there have been close moments between Naruto and Sakura, just out of the majority of them they always ended too soon but for the sake of comedy.
Take note:
-Reunion, Sakura asks if she looks more mature, Naruto responds you have not changed- he messes it up
-Sakura admiring his maturity but they he wants to reveal his new sexy jutsu- he again messes it up
-Sakura crying and happy Naruto is alive after the 4 tails event, Naruto overreacts again messing it up
-Sakura is recovering a bit and Naruto mentions how amazing she is but it ends as soon as he mentions monster strength
-Naruto is struggling to eat but Sakura offers to feed him but Sai interrupts
-Sakura was about to talk to Naruto right after Sasuke left but before she could say anything the posion kicked in and knocked Naruto out- a misfortune.
When a lot of closeness begins to come, something cuts it off. The only one which went off entirely was the hug to which it was mutual on both sides, Naruto was surprised Sakura did that (something he thought would never happen) and Sakura was truly thankful to him for saving the village, she still hit him cause he was acting reckless to do it all on his own but she was truly happen for him saving them. She hugged him out of thanks, not jealousy from Hinata as many anti-fans say.
Still many many moments of closeness despite their other feelings. NS is different because of both of them doing so much for each other despite a struggle on both their parts. Naruto tries to fulfill Sakura's happiness despite knowing it could ruin his chances and does not take advantage of the face Sasuke is gone. Sakura tries to do things better for Naruto and tries to help him and understand his pains despite still loving Sasuke. The key player in this though is the larger interaction and such.
For NaruSaku the feedback interaction between Naruto and Sakura is heavy, its the most occurring.
For NaruHina the feedback interaction is still there between Naruto and Hinata but its still limited and rare from Naruto to Hinata. Its still mostly Hinata to Naruto.
For SasuSaku the feedback hardly existed, the good interaction ended with Sasuke leaving the village. It literally was always one way from Sakura to Sasuke never back. The only recent interaction was kill attempts from both sides. With both Sakura and Sasuke having attempted to take the others life, it should not come canon even with Sasuke being redeemed, I mean if this whole attempts on each others life thing manages to pull bs and get SS as canon, it would simply have been "a rough moment in their relationship"

Seriously? This is what SS would be pulling if it became canon and managed to destroy both Sakura and Sasuke's characters.
The main point is, NaruSaku has the interaction that has taken them on the journey and brought them through some of the best and worst. As I said before, NaruSaku is more about the journey, something that was only a hope for Naruto and unpredicted for Sakura but it happened along the way. NH and SS at this point are just destinations, if they come its just due not going to be good because they don't have that development like NaruSaku. NaruSaku is along the journey and just will occur at some point, it can, the path of the story allows it, it is one element of a good ending for the story, good ending development for Sakura and some important parts on Naruto. It does no damage and fits, kishi just needs to make it happen.