Hm. Delta squad can't go rogue, but if they would, Sev would probably go first, since he's a bloodthirsty psycho already. And since he's the one that's missing, they might work it out a bit.
It would be nice if you could fly along in a gunship gunner-bubble and gun down enemy droids as you zoom over the battlefield. Y'know, a sort of minigame.
Driving those republic speeder tanks would be neat too, but then it wouldn't be the same game anymore, I'm afraid.
playable Jedi don't seem like a good idea, but encountering a Jedi, ARC trooper, or another pod of commandos would be nice.
I think it would rule if they made it a bit less linear. Instead of having to choose how to open the door (wich didn't even really work much anyway, as enemies always noticed you when you stepped trough) you could choose between going trough the door, or crawling trough an air vent.
That's all i can think of right now.