If you are to believe "the internet", Win10 will take control over win7 since it will use win7 key to update to win10 and lock that key to your machine.
I am unsure on how taht exactly works but does not sound good to me.
Win10 also forces you to auto update (no telling what they will come up with in the future) and you lose your win7 key since its converted to win10.
As far as I can tell DX12 aint really working yet (most tests are inconclusive), so going for DX12 reasons to win10 seems a bit premature.
What I don know is that compatibility issues are showing up here and there so If it aint broke, dont fix it is the motto Id go by until there is a legitimate reason to update to DX12/Win10.
I also dont like that Microsoft is giving Win10 "for free". There is no such thing as "free" because youd be asking Microsoft workers to work "for free", etc....
I should probably read the full agreement with WIN10 licence but to be honest I am not yet interested in Win10 so i simply skipped it.
You might want to read the agreement yourself and see at least what they are not saying loudly, but sure is public knowledge.