Yes frame gen could theoretically bring a 30fps locked game up to generated 60fps. But most of these older games won't have the data required by frame gen (per pixel motion vectors), or even if they do have that data it can still be a lot of work for modders to add frame gen support.
AMD has a driver level version of frame generation that doesn't require the game engine to provide motion vectors, but it's much simpler and similar to TVs that have motion interpolation.
Based on FSR implementation and rumours AMD may ditch high end and enthusiast GPU market altogether, I would not put my money on the tech, Best we can hope for is nvidia upgrading the RTX remix to make the implementation even simpler for modders
remember RTX Remix only works for fixed function graphics, so games like Doom 3 with programmable shaders will not work in RTX Remix
Half-Life 2 was mainly programmable shaders, but it had an option for fixed function graphics for older computers, which is how it works in RTX Remix
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