And as much as I'd enjoy Caribou being revealed as a revolutionary (his cover story + the revs are my favorite faction), and two, think he's just gonna be working with Blackbeard (lamest possibility tho imo), the possibility that seems to me to be the most "favorable" with what we currently know, is the whole Mr. 10 Cross Guild theory. Maybe he stumbles across some interesting information (that either few or even no other living beings are privy to, the latter only making sense if all the vegapunks died or if vegapunk dies and had placed some kind of memory block on whatever this info is), important blueprints or special technology. As for other possibilities, he could steal a certain person, be the one to save some important object thought to have been destroyed by the beams raining down on Egghead, have him safely stash away the straw hats that are currently petrified (if they dont get returned to normal while everybody is still on the island) or have him pull a heroic chekov's gunman, especially if Oda is actually insane enough to make him a straw hat.
I'm not saying that's what I think will happen, because I really have no fucking clue, but it's all I can come up with atm.
