TMBTM said:

As much as I'd like Peter to play Chewie again (if he can physicaly do it), having him "filming" something in may do not mean it's Episode 7; and even if it is for Episode 7 it could also be an unmasked cameo (and that would be sweet from J.J to do that kind of thing for Peter, IMO)

Good thinking, as THAT would be a 'cameo' appearance I'd be happy to see, if he can't physically play Chewie again. Warwick Davis was seen in the crowd scenes in TPM, and I'd be pleased to see Peter Mayhew get a brief moment too in that case.