While I do agree that having a single common trunk is the best option, I'm not sure I agree that spawning several slightly incompatible QT-derived tool kits would be good for MS. We are talking about developer tools, each with a different name/trademark, not OSs.
I doubt this too, frankly. But, it is possible. I just don't think that the benefit they would get from it could compensate for the level of threat of having a viable, top notch, cross-platform, tool kit in the market.
The worst thing for who? For MS? I don't think this is their worst case scenario.
I could live with this scenario, but I am not sure it is the best that can be had.