I am in the minority for not liking Wolverine's cameo in the first movie. I'd much rather have a nod to someone else or see a young new mutant. We already met the elder Stryker at the CIA. It might be nice to have him tied into some evil government conspiracy.
I still can't think of a good sequel title. I'd rather simply have it go hehe rogue and just be called The Brotherhood of Mutants.
Interestingly, who would you not want to return?! I say Emma Frost and Angel most definately. I wouldn't mind having Havok and Banshee be there, so long as there was a new mutant or if they all had some development. The problem with the first one was too many tossed in mutants.