Nvidia recently started NVK for Turing and newer and even more recently it was made conformant going back to Maxwell, but that still doesn't give me a lot of hope for everything between Maxwell 1 (so basically just the GTX 750/750Ti for desktop Maxwell 1 cards) and Turing after driver version 580.

Also, Nouveau works for Maxwell 1 and earlier but ymmv with that stack, and it's still not like Mesa RADV and AMDGPU for Radeon cards going back to GCN1.