I finally read
this which contains a quote from presumably the Microsoft lead on this subject ("Max McMullen"). Of most significance to me:
Max McMullen said:
Why D3D12 on Win7? We’re at the next stage for D3D12 and low-level APIs in the technology adoption curve by developers and publishers. The next order of magnitude in the title & engine population are now designing first, or *only* for low-level APIs.
The prevalence of Windows 7 and the need to support it to maximize market exposure is prohibiting the adoption of D3D12. The low-level framework of D3D12 is not backwards compatible with Windows 7 which is stuck on D3D11...
This makes me think that Blizzard only pursued creating a D3D12 renderer because they got assurance from Microsoft that it will benefit Windows 7 gamers too.
...so yeah...look at games like The Division where it claims to be DirectX 12 but there's no performance benefit really to speak of. That's what Microsoft wants to stop. Everyone should be targeting low level APIs (be it D3D12 or Vulkan) so this move is Microsoft trying to make that happen.
Microsoft wants to retire D3D11 and older just as bad as they want to retire Windows 7 but they can't do that when so many people refuse to upgrade to Windows 10 so game developers are put in an awkward position of balancing priorities:
Max McMullen said:
There’s a measurable population of gamers in some markets that likely won’t get off of Windows 7 in time for this next wave of titles and engines on low-level APIs. D3D12 on Windows 7 is what my team did to assist developers & publishers with the engineering cost and addressable market tradeoffs they were making.
...expect more D3D12 exclusives soon that will run on Windows 7 and Windows 10.