I suspect that this is exactly what's going to happen. If RasPi gains significant traction in schools, either MS will get a "subsidised" Win CE/Embedded/Mobile platform out to schools for free, or there will suddenly be a port of one of the embedded Win platforms for the Pi. Either / or will be "sold" on the grounds that they are "standard", and "work within existing infrastructure".
Yes, I'm a depressing old cynic.
And as another commenter said, probably correct
There's ample precedent for MS moving to squash any computing movement that might pose a threat to it - remember the netbook? I don't mean the "small laptops" we've seen in recent years: I'm talking about the "real" netbooks, like the OLPC and the Eee 700-series - compact computers for use in schools, with solid-state storage and a Linux OS. As soon as MS realised that these machines were taking off, and that people wanted them... well, you know the rest.
Assuming the R.Pi "takes off", especially in the education market, I reckon it's a matter of time before MS wakes up and moves to head it off, somehow. I want an R.Pi before that happens...
(BTW: almost every time people see me using my Eee 701, I either get asked "wow, that's neat; where did you get one?", or "isn't it too small?" I expect I'd get that even more if I owned an R.Pi )
Raspberry Pi Model 3B+ (2019) ("ayeka") - CentOS
Raspberry Pi Zero W (2018) ("mass") - Raspbian
Raspberry Pi Model B (1st-gen - 2012) ("ryo-ohki") - Arch Linux ARM