How hard would it be to support more down-level graphics hardware in the Direct3D 11 driver?
There’s a page on MSDN which covers restrictions relevant to supporting feature levels 9_1, 9_2 and 9_3 in Direct3D 11: https://msdn.microsoft.com/en-us/library/windows/desktop/ff476150(v=vs.85).aspx
WinUAE recently added support for D3D11, and while the initial beta versions required feature level 11_0 hardware, the developer was able to support feature level 9_1 in the release version. That’s great because it probably covers all hardware introduced since (at least) 2006/2007.