I don't know how "easy" it is to implement frame generation but I tried the Luke mod on Nexus and I don't know if I did something wrong but the game looks horrible with that. Flickering textures all over the place, especially the vegetation when I was moving. So I removed it and installed the DLSS 2 mod and that works fine, but of course I get less fps. I found online that some people got more luck with the DLSS 3 mod by changing the default preset in the json file. I may try that but if the game gets the official DLSS 3 support soon it may not worth the trouble.
Anyways, it's a shame that this game is so hard to run with those dated graphics. I play in 4k so I didn't expect 200 fps but my 4080 can do much better with other games that look way better than that. But the GPU is not everything in this game. I noticed that when the frame rate drops a lot, mainly in big cities like New Atlantis and Akila, my GPU load drops to 70-80% and my CPU load increases to 50%. When the frame rate is good my GPU utilization is above 90% and the CPU is in the 30-35% range. So looks like there is some CPU bottleneck especially in cities, maybe because of the NPCs walking around, but as for the graphics, other games have bigger cities that look better with more NPCs and my Ryzen 5900x has no issues handling them.
Poor optimization or limitations of Bethesda's old engine? I don't know but hopefully things will get better before I finish the game (and it's so much fun that it may happen soon).