Rumour has it that Ford's deal is a fairly significant part. I'm not sure that he'd be interested in just a cameo, to be honest. He doesn't owe Lucas squat, and has done so much since then that he barely remembers those movies, so if he's on board, it's because it's worth it for him to be on board. Sure, his role won't be as significant as in Crystal Skull, obviously, but he'll get a few action scenes and lots of dialogue, I'm sure.
I just hope he's still flying the Falcon. It's not a Star Wars movie without the Falcon breaking down (again).