has confirmed that it's real. (Apparently he's playing Dogberry.) And then so Maurissa Tancharoen did too. And of course Whedon has spoken often in interviews of the Shakespeare reading groups he does with his friends (including people he casts in his TV projects). So I'm guessing it's legit.
So, uh, yay!!
Update (10/25): So this news is everywhere now -- like, even in the newspaper of record. (Are they still that?) Unsurprisingly, Whedonesque is the place to go for all your MAAN news. The juciest single news source I've seen on it is this interview with Whedon, Sean "Dr. Tam" Maher and Amy "Fred/Illyria" Acker. Apparently the film is in black and white -- which is cool (I wonder if that was a purely aesthetic decision, or if it was also financial?). And it was shot entirely at Joss's own house -- which, who knew, was designed by his wife Kai, who's an architect.
The full cast list is in the official press release, but I'm going to quote this blog post which lists the actors and parts along with Whedon-fan-friendly identifications:
Amy Acker (Angel) will play Beatrice and Alexis Denisof (Angel) will play Benedict. Fran Kranz (Dollhouse) will play Claudio and newcomer Jillian Morgese (The Avengers) will play Hero. Nathan Fillion (Firefly) is Dogberry, Clark Gregg (The Avengers) is Leonato, Reed Diamond (Dollhouse) is Don Pedro.Additionally, Sean Maher (Firefly) is Don Juan (the villain of the piece), and Tom Lenk (Andrew from Buffy/Angel) plays Verges. And that's it for Whedon alums that I can see on the list.
I don't know Gregg, 'cause The Avengers hasn't come out yet, or Morgese, 'cause she's a "newcomer" (how'd she get so lucky?), but the others are all fun to imagine in their respective roles.