You know what would be a lot easier than this? Make your own party. Kick out people you think suck, or w/e and grab someone else, no programmers, designers, or scripters required. It takes a pretty short amount of time to see if someone is lagging behind due to mechanics or DPS. Any time wasted at that point - either from you letting them stay, or staying in the group, is only on you. That isn't anyone else wasting your time, that's you sitting in a fight, raging, boiling over, wasting your own time. I guess if people really want something like this for DF, pug data center grps then fine. (Not you specifically, I'm just saying in general.)
I'm glad you are at least thinking of some specifics here, in how it could work. It still boils down to being an "Educated Assumption." One that I personally don't think is needed, nor do I think it will address any of the issues people are concerned with here, save maybe a few dudes that just can't get past it. It just turns into a smaller pool of players that care, and a bunch of false positive results... Everyone is entitled to disagree on that point if they want. The thing is, anyone that already wants to get better is already trying to get better.
It puts a lot of faith in this "test" for a very specific and most likely unrealistic result. (Less "bads", better play, less wipes etc...)
Anyway I hope that makes more sense, since people are obviously not understanding me here, and seem intent on explaining things to me that I already understand just because they are not understanding my point of view.
Again I would rather throw my weight behind a system that allows you to chose a fight, and work on it, by selecting phases etc... We already have dummies.