[midoridensha]

>Maybe I could take the aqui-hire angle, but how many Ubuntu devs would want to stay with Microsoft?

Probably far more devs than they'd get trying to make their own MS-branded Debian from scratch. Even if a bunch of them left after a while, they'd have competent, experienced people working for them for that time, instead of trying to staff up from zero and having a lot time where there aren't enough people to really get much done, and during that time they can hire new people who aren't going to quit just because it's MS.