ZDoom

It's not that easy to implement because GZDoom does not save data between frames which is important for an implementation like this. Plus it also needs a lot of other data in order to function (such as vertex shader info) which is not readily available.

If it was easy to implement, I'd say give it a try and find out, but it looks like implementing this into GZDoom wouldn't be as straightforward as it is for a modern engine. I just figured I'd bring it to your attention.

While this is cool tech, I have a feeling it would struggle with our use cases as it relies on coherency between frames, for example a monster making a 45 degree turn is probably too much for it.

This is way out of scope for a Doom port.

With AMD releasing FSR 2.2, I'm wondering if it'd be possible to implement into GZDoom?

https://github.com/GPUOpen-Effects/FidelityFX-FSR2

If anyone's interested in looking at it. I'm not going to call this a full feature request, as I'm not entirely sure there would be a benefit to VRAM usage. In my mind, there should be, but I don't know enough to really make that claim.

Check it out, though. At the very least it's an interesting repo to browse.