Though he hasn’t heard anything from Lucasfilm, Frank Oz would be willing to return to voice Yoda, according to Hero Complex. But don’t expect another puppet version:
“I think it depends on the story, but I think at this point you can’t go back to the puppet,” he said. “The reason George [Lucas] did the CGI, which I supported, was that he wanted to tell a story that would have been hampered by the physical limitations of the puppet.”
However, remember that while it’s been confirmed that there are spin-off plans in the works, the Yoda film is still just a rumor.
Love Frank Oz, don’t like Yoda anymore. His point of view in the prequels made me want to hit him repeatedly. “Dangerous and disturbing that puzzle is.” Oh really, Yoda, thanks for stating the obvious here. “Rejoice when everyone you ever loved keels over.” Just shut up, you little green freak…
Stupid prequel Yoda… *argh* ;-)