I really think the days of the Muppets has passed, at least as far as movies anyway. I haven't really enjoyed one since the second or third movie.
But I do think it could work on TV again, if done right. It would be hard, though. While I actually liked Muppet Babies, you would really need to get that out of your head. The original Muppet Show had an adult wit that grown ups could relate to, good music, and great guest stars. If you tuned into The Muppet Show thinking you were going to get Sesame Street, you were sadly disappointed. It was so much better. They need to bring all that back. I like the idea of a variety type show better than some kind of muppet sitcom.