It takes time to press and ship games. They have to be done at this point and just testing.
There might be time to add in a new move if it premiers this week or next in the manga, and obviously there are probably plenty of characters they just haven't announced yet, but nothing new will actually be made at this point, they'll have finalized their roster 6 months ago. Sabo getting the fire fruit in chapter 750 seems a likely cutoff point for those decisions.
That said, even if Bart is in the game, (If the popularity poll had hit a month or two sooner I'd say it was a sure thing… but he'll definitely be in 4) I don't think they'd bother doing that last minute new move for him the same way they would for Luffy or Zoro. Maaaaaaybe Robin's new move since she so rarely gets anything, and if they already have next week's chapter to work from.
If this game is as thorough as is appears it's going to be there will probably be different versions of characters from different areas of the story, for example, East Blue Luffy this version of Luffy would consist of techniques he knew between Captain Morgan arc and the Baratie.
Point is perhaps a second version of Barto could be added as DLC.
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Looking forward to seeing Tashigi, wonder what Alvida moveset is going to be we haven't seen her do much.
she still wields her mace so that will be apart of it. she will also probably be pretty mobile via her slip slip fruit powers