To be honest regarding Kinkaku, Ginkaku and the Swordsmen I started to doubt their status as playable characters when we never saw them outside of the Hack and Slash mode, they're similar to the other paths of Pain that you fight as Jiraiya in Storm 2 in that regard (you could not use them in vs and even that Jiraiya you played as was completely unique to that battle).
The Kage though there is no excuse, everything they have shown pertains to a playable status. They have grabs, jutsu, combos, ultimates, the works, combining that with some oddities in the placement of characters here's what I think.

There are 2 Chouji's even though 1 just has a different awakening, there are 2 Gaara's even though he just has a different ultimate and jutsu, there are 2 Itachi's (edo) even though he just has a different ultimate and there are 2 Bee's (he at least has a different moveset). But it is incredibly inconsistent with other characters Guy, Kakashi, Naruto and Sasuke all have different selectable ultimates but they share 1 slot, the Raikage apparently has a selectable jutsu but he has one slot. Chakra mode Naruto and EMS Sasuke have 2 COMPLETELY different movesets on 1 slot.
It makes me think all the multiple characters except Naruto and Sasuke (because Naruto and Sasuke) were meant to be 1 slot each and the 4 extra spaces were meant to be the Edo Kage but something happened at a corporate level that decided to take them out with the sole intention of selling them as dlc later on, similar to Dampiere in Soul Calibur 5 or the 12 extra on disk characters in Street Fighter X Tekken, considering they are shown to have everything needed to be playable. The taken out levels could be in the same boat.
Though I could be (and probably am) wrong and they will never be playable.
Even though it's incredibly disappointing, lazy, greedy etc I'm still going to get the game because to be honest I never play vs mode the only time I do is when I have friends over who also like Naruto (very few) and I have never touched online, so I'm getting it for the Story Mode and considering what I've seen of that it looks worthwhile.
On PTS though why is Hinata there? Sakura may have not done much in terms of fights but shes Team 7, I guess Neji's there for Sasuke retrieval and to beat up Hinata but he's also an odd inclusion. Like when I think of important Part 1 fights Hinata vs Neji doesn't spring to mind, Shikamaru would seem like the better choice.
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I was going to buy storm 3 but what keeps me avoiding the fact to buy this game is that the arc didnt ended so the end of sotrm 3 will be before the final battle which is not the best way to end a game before the end of an arc.
Moreover with the launch of Playstation 4 it's kinda obvious they are going to launch another Naruto's game next year but with a new engine since this one does not support PS4.
I totally understand what you're saying, its a problem that pops up every new generation but even though there's a new Playstation and Xbox coming this year I don't think we will see another console Naruto game next year, PS3 came out 2006 but Storm 1 didn't come out til 2008.
But I do think this will be the last Storm game, whatever comes next will probably be at least starting back from the beginning of Part 2, (hell they might even do another Part 1 game again).
Even though the war arc hasn't ended apparently Storm 3 has an ending, the Kage's beat Madara, Naruto beats Tobi, unmasks him and then Obito runs away, everyone goes back to their villages, war over. I'm not joking, I think they decided that this would be the last Naruto game of this generation they couldn't end on a cliffhanger.