I'd be willing to bet that both Charlie (NUnit lead) and Jeff (MbUnit lead) would be more than willing to take a sizeable "donation" (perhaps as little as 10% of what the MsTest devs got paid) to their projects in order to provide a stable source version for MS to review line by line, under whatever license they decided they wanted (as a fork of the projects) in order to include their projects with the release of visual studio. I'd even be certain that both projects would have jumped at a chance to have pre-alphas of visual studio to integrate with (for full compatibility when the first beta hit the market).
The only thing that is stopping this level of cooperation is lawyers inside Microsoft (and the occasional prick of a developer), and for that MS deserves our pity. I think the only thing that will get MS to open up is if they were to come under so much financial stress that they could no longer afford the lawyers (and only open source appears to have that much power).
Some time ago I had a discussion where a developer within Microsoft explained provided myself and the others in the discussion what he felt was MS's viewpoint:
"From the Legal Dept's perspective, it's not merely the license the code was released under, it's also the heritage of the code. If some evil coder had stolen code IP from a source base, added it to a project with an open source, copy-reuse-repackage freely license, and I used it, the original IP owner could still sue me to get me to desist using their IP. So, in the interest of protecting corporate code from this sort of legal attack, Legal usually has to perform some pretty thorough (and thus also expensive) investigation before letting anyone see open source code; you can imagine that there generally has to be a good business justification before that kind of thing happens."I think that opinion is rather unintelligent, but then again I'm not a paranoid lawyer who thinks everyone is out to get me (certainly I'll concede that there are a few people out there who are).
As far as TFS goes, what little experience I have with it tells me that it is too complex, has too many moving parts (all the more places for bugs to find their way in) and is too constrictive on my working habits. I'll stick with Mercurial, thank you. And wherever that isn't available, Subversion will have to do. I like my environment to be compartmentalized. That is why I'd suggest to use Mercurial, Bugzilla and CruiseControl.NET (all of which integrate nicely with each other or are easy enough for me to write my own integration).