People are blowing this out of proportion.
It was a hypothetical question thrown at him during an interview. "Would you do Batman again?" All he said was "yeah, sure, if Burton was directing". That's it. He was being factitious. The guy doesn't need or care about Batman really. He's gone on to say that it was just a role for him and that while he's fond of his time in the role, he's since moved on.
There will never be another Keaton Batman film, ever. It'd be inappropriate and pointless. The closest we'll get to that collaboration is the sequel to Beetlejuice which is slowly coming into fruition.