@ex720:
I don't know if this has already been talked about, or already had anything announced to this respect, but what would be the chances of this game including the first part?
It'll include all the stuff that was in the first game in some form or another, though the actual level layouts will probably change, and probably movesets will be tweaked so the characters won't play exactly the same (which would be a good thing in many cases.)
If we're lucky, they'll drop the adventure stages idea entirely and turn them into regular stages (and thus everyone could play them and no awkward Sonic Unleashed style platforming.)
Its how Musou games work. They stockpile and tweak assets over the course of many games, and so by the third or fourth game they have a huge cast and number of levels.
They just haven't announced any of the old stuff because… that's not exciting.
So expect Jinbe, hancock, Ace and Whitebeard to be playable... and presumably a whole handful of enemy characters that were in the previous game, but weren't playable a the time.(Being playable is news, but the character being in the game isn't, so it doesn't get ad space.)
However, be prepared for the bizarre anachronism of everyone being timeskip designs in old story stages.