Also, is DX12 really a requirement??? What about old PCs which don't have DX12 support?
It's been a very long time since DX12 came out, most systems in the last ~5 years are DX12 compatible due to the APU.
Nvidia most 500 series on mobile, pretty much all 400 and 600 series and newer, that's 2012 or so and newer.
AMD the FirePro from 2014 for workstation and newer, "gaming" side think the R7 250 was the oldest/worst that supported it, unsure, pretty much anything post that supported, that's 2013. Most of their APU's had it 2014/15 as well, not sure there, those are a recycled mess.
Intel HD 630 or newer definitely had it, from 2016 onward, basically when they moved to 3 digit nomenclature, which was Skylake AFAIK (CPU 6000 series).
And then W11 will mostly just be new systems, plus W10 still has support for another 5 years, by the time forced drop happens those "youngest" systems will be 10 years old, and lots hitting 12-14.
Based on 3D stacking and other changes, I think we should probably see a nice performance increase in the next 2 years, including power consumption, just look at the last 3/4 years in regards to how much the power use has reduced in laptops. It will basically be at the point of why are you still using such an old system now, it's doubtful we will have another sandy bridge case of no real performance changes in 7/8 years.