I actually come to this topic with some big news, some being what people have been waiting for actually~
Looks like all this Marineford stuff we've seen so far is actually an entirely new mode, not a new island. Everything on the island is seen on a map, much like the Story Mode of Gigant Battle. You start out at the beginning of the map, select a point, and you'll engage the story at that point. You beat that, and more points open. This mode has also confirmed their own cutscenes, mostly just 3DS remakes of the events of Marineford. If you look closely to the map screenshot, you'll notice Oars Jr. What I hope is that you'll fight him the same way you fought Oars, him basically being a reskin.
These scans also confirm that Akainu is now playable. Crocodile, Buggy, Aokiji, and Blackbeard have all been updated to their Marinford selves. Jinbei and Sengoku appear, but it is unconfirmed whether they'll be playable. Odds are Jinbei will be atleast.
All this news almost deconfirms Foxy and Magellan though.