Would it be relevant at some point to just stop calling it the new NVENC? Eventually it's just going to be what's current, doesn't it make more sense to name it NVENC (nvidia) and rename the old one to NVENC (ffmpeg)?
Also, does the new nvenc only work with driver version 4xx.xx and above? Or can you use drivers as old as 3xx.xx? I thought you needed the "latest" drivers (again, define latest? same issue with calling it "new", it's only new / latest now, it won't be true in a year). I'm using 388.71 drivers and the "new" nvenc still shows up. Are all the optimisations inside OBS itself and it works with any driver? Or were my impressions correct in that you need the "latest" nvidia drivers for new nvenc to function? If so, it makes sense to hide the new nvenc option entirely if unsupported drivers are detected, just as it hides the amd or intel encoders on unsupported hardware.
Also when "new" nvenc is selected, the rescale option box is un-checkable, I know why, don't explain it, but it makes more sense to just hide it like is done with the look ahead and psycho visual boxes when you switch back to the old nvenc. I feel many new users will try to click on that rescale box and be confused as to why it's not working. Just hide it for the sake of confusion. Replace it with a label with the output resolution if that's the only reason it was chosen to keep that box / dropdown there.