Sorry for not replying sooner. Since the latest nvidia drivers now have beta support for VMs, I have gotten my 1070 to work in a windows VM in qubes 4.1 (and I imagine it would work in Qubes 4.0). Nothing special to make that happen besides rd.qubes.hide_pci so qubes doesnt use the graphics card. I did not use the gui domain.
The issue now is allocating more than 3.5 GB of ram to the VM, making sure disk performance is good, and possibly sound from the VM.
The ram issue supposedly has a work around but I cannot get it to work in 4.1. I have not tried 4.0 to see if I can get it to work there. See these threads:
https://github.com/QubesOS/qubes-issues/issues/4321
https://forum.qubes-os.org/t/another-2-gpu-passthrough-post/2821
Edit:
I also tried a debian VM with passthrough and had the same issues of it not booting with more than 3.5 GB of ram. So the TOLUD change regarding ram did not seem to work in 4.1.