Maybe they could consider an Apple-style approach: open source the core of the kernel and text-mode user space but leave the GUI closed.
Of course, open sourcing everything would be even better, but that might too big of a step for them. Open sourcing the non-GUI core could be a good initial step, whether or not it ends up going further.
my guess is if they did it it would be under some odd ball license just to make sure its code couldn't be incorporated into other penguin themed operating systems
Calculator (the horrible UWP one, unfortunately): https://github.com/microsoft/calculator
As for that FAT driver, it was traditional to include in the SDK/DDK sources of some of the actual drivers in Windows, so that one is not a surprise.