If windows 10 and office365 hadn't rubbed me wrong, I'd probably be OK with it, at this point I'm stuck on the Windows 7 sinking ship watching my options blip out,
Now Microsoft actively uses github in house heavily, So at a guess, they cannot do any large sweeping changes without annoying your own in house programmers, This should keep the functionality side similar,
Privacy of IP, that is more concerning. Not to mention it will probably give them insider knowledge on its competitors, e.g. what new features they have been investing time into.