Currently a discussion is going on when and if Mist will be released at all:
It would clearly be interesting to have a market on this. One challenge will be to define "release". What features are necessary to call it a release. What degree of bugs are acceptable?
Outcomes could be: Within November, Within December, ...
Think you are setting yourself up for problems with these "hard to resolve events", if they relese a closed beta some people will proclaim it's a release and some will not. Better to start slow so the site doesn't get into trouble. Then when anyone can create events, they can do whatever they want.
Yeah, the key is to specify the conditions very precise upfront:
At least binaries for: Windows 8+, MacOS, Ubuntu, ... At least a list of features. But you are right - it is a tricky one.