During the last beta, people threw a fit because they couldnt run anything at all.
The problem was (in general, I know there were exceptions) that most people who couldn't run anything got frustrated and left
without providing enough feedback. Also many players refused to go back and try it again when HTC made updates. So I can see from HTC's perspective that it was more hassle then it was worth, with little return.
In my opinion, if HTC were to do something like that again (either public or private) they would have to be convinced that the extra work (for them) is worth it. That's why I feel it needs more structure on the players side, to show that the time and effort can turn around problems more quickly and clearly.
As an example with the current sound situation, they would have to depend on, hit or miss, to find any issues. Whereas with a structured test environment, they would have a better documentation of what systems were used and how they performed.
And one last thought, software testing is usually pretty boring. Expecting everyone in an open environment to stick with dull testing, vs. flying with their friends in the MA it's easy to see which one most players would choose.