Eh, I don’t think you understand what they’re doing. Give the PPT a read. The entire point of using the previous raw frame input before any other post processing was done (like that frame’s FX+TAA) is to avoid infinitely duplicating old frame data that has already been run through post process AA methods. This inherently avoids the entire possibility of ghosting beyond 1 frame, which even then is masked through some of the other techniques they detail in the presentation. The ghosting we see in UE4 partially results from the fact that one frame receives TAA, then the next frame uses the last frame’s post-TAA result, then the frame after that uses that last frame’s post-post-TAA result, etc. recursively duplicating past frames infinitely. The oldest frames’ contributions become smaller and smaller for each new frame, but you still end up with ~30(?) frames worth of old data getting smeared around as the TAA continually stacks older and older post-TAA frame data.
Also I have to question if you’ve bothered playing it if you think it looks bad. Running on old PS4 hardware from 2013 they’ve achieved silky smooth AA without anything remotely close to the kind of ghosting I’m used to seeing in UE4, and the reason they went with this approach is because Horizon:ZD is basically the worst-case scenario for TAA. The entire game is filled with tiny sub-pixel grass, foliage, and hair, all of which is moving constantly.