I don't see why they would? Windows 7 is already by far and away an inferior gaming os up next to windows 8/8.1. Not to mention an old os as far as they're concerned. I can see win 8+ getting dx12 love, nothing below. W9 will likely be the same back end/kernel as 8/8.1.
My windows 8 update pack cost me £25 direct from microsoft, if £25 is too expensive you're on the wrong gaming platform I'm afraid.
ok this is not about me, i paid for my windows 7, just saying.
but the point is, are we looking to have dx12 as a default api used on all games ? if yes then this wont happen untill it has about 40-50% user base, otherwise devs wont even look at it.
but if you are looking at a couple games per year for the next 4-5 years like for Mantle, then yea why not, make it windows 9 exclusive, put DRM account based, and lets buy win9 and all wait up untill the user base gets the treshold needed for devs to start using it, which wont be 2016 not 2017, or 2018, all these years will be few financed games by microsoft or nvidia each year.