From what I remember, the Muppet performers were very interested in an event like this, and many of them were on-board from the start. Although a problem came up with Henson, I can't understand why they would ever shoot it down again. It will take negotiating and certain needs will have to be met, but I think in the end it would work. The main issue would be on how we can get all the properties in one place and have all companies agree on it. Something I would have thought was impossible until that Jim Henson Musical World event at Carnegie Hall two years ago.
It will take a lot of work, and the support is certainly there. I think it's still possible. Even if we don't get the agreement from Henson/Disney/Sesame, Toughpigs hosts Muppet Vaults once a month which I'm pretty sure are not cleared with the companies, and is allowed from a legal perspective. The hard part would be having the characters live in appearance, where the paperwork could get heavy.