Would it be possible for Crocodile to be released from Impel Down?
The World Government has him in custody, the World Government clearly is of the concern that Ace will not be executed - Thus the calling of all Seven Shichibukai to help the Marine Headquarters make sure it happens.
He is clearly still at the 'level' of the others, and it would be a 'waste' to just keep him in there - Especially if things go 'wrong' (Whitebeard's coming).
I also thought of something Luffy said : "If you're the Shichibukai, than that makes me the Hatchibukai" - A joke meaning Luffy would be the 8th, Interestingly enough - Crocodile IMO could just be that 8th. Just because the spot was filled and he was demoted does not mean he cannot be of use to the Government.
If they are willing to make a deal with Pirates to begin with, Everything is fair game.
1. The people would not have to know about it.
2. Striking a deal with Crocodile would probably be within his interest aswell - He could make up that Hatchibukai crap as his own thoughts. lol.
3. He can be an asset on the battlefield, according to Yellow Book there are 16 divisions (I think it was yellow) of Whitebeards crew.
Thoughts? Is my theory to farfetched? I like to call it thinking outside the box, Just because the Government has 7 spots, does not mean there cannot be 8 - Especially since it WAS said in the manga before, and Crocodile is a fomer Shichibukai, as well as in their custody - AND the Execution MUST be done on time. Whitebeard > Single Demoted Pirate in terms of importance.
A deal could be striked..