I think that it would do them good to have DISNEY and Final Fantasy villains as the thirteen darknesses. I can see DISNEY opting out of that, but I do feel like this is a perfect opportunity for the game to try to go back to its roots. There's already been a good job of cleansing away lots of the original characters in the series, I think it'd be a cop out to just bring back ones that we thought were dead.
I would like to see Riku Replica there, as I thought he was still alive, but apparently he was killed so... yeah. I can definitely see The Evil Queen, Man, and Judge Doom as darknesses. I'm not sure what other DISNEY villains can really fit the bill, especially ones that we haven't killed already.