I won't be joining.
A) Disney's track record with these things. Remember the MKC: they used to use it as perk for their shareholders that you had to pay a little bit extra for...that went away. So did the Disney magazine....
B) Disney's events for fans usually turn into an exclusive merchandise event. I am a survivor of DL's POTC 2000 event. Completely sold out, and after the previous summers' problem with the Haunted Mansion event, they changed everything to make it more fair to buy the exclusive merchandise. (HM was first come first serve, and eBay was the #1 destination for the goods) People were on Main Street til the park opened the next day to get their merchandise...one line. And it still wasn't that exclusive unless you were buying the expensive stuff. Things like the VR "walkthrough" of the ride ended up on the Black Pearl DVD. And the CD was released to the general public.
But to be honest, this was inevitable. When Mousefest got big enough it would attract Disney's attention, and Mousefest just got too big to be for free and run by volunteers. Naturally, who has the pockets to have those kind of events? And do they actually do things for free? The D23 gala thingy at DL is interestingly starting right after their next HM event, which at $400+ a pop, seems odd in the current economy, but it sold out quickly.
And the last thing...will the D23 community go contrary to the official stance on stuff? There was a huge outcry and attempt to stop Disney from implementing IASW Under New Management (I'm withholding judgment until I see it in 5 weeks), so what would D23's view be? Having an official Fan Club is one thing...but making a community with the expectations of Web 2.0, and opinions of those who are members may be interesting to watch. Perhaps I should join and get some popcorn.... ;D