Do we know what AA Horizon FW uses?. I think it could work, but I'm left wondering about the abundance of foliage the game has and how it will look. I imagine FW will be a real test to see how 2.0 would deal with jaggies and smoothing.
As long as it doesn't have aggressive TAA, it should be fine, though with the advent of TAA and devs using slightly different variants of it these days has got me wanting devs to just agree on using one version of it for FSR's sake.
Horizon renders in checkerboard mode first, then upscales the result with sharpening instead of TAA. That gets messy when most of the screen constantly changes with foliage moving in opposite directions in front of each other. Especially with a sharpening filter on top to make the edges stand out after upscaling.
FSR uses motion vectors to help with temporal reconstruction. Yet I imagine there won't be a motion vector for every single leaf and blade of grass waving about in the wind. It would be very computationally intensive.
TAA removes this high frequency detail. FS2020 uses quite an aggressive form of TAA which removes small details, like small lights, windows and highlights. You get that detail back with supersampling, render at 4K, downsample to 1080p, but that's quite the opposite of trying to gain performance :) Yet super sampling is the only way to solve the softness vs noise conflict when you have lots of fine detail like foliage, power lines etc. And as seen with Horizon, double the frame rate, double the shimmering. (Of course the lower base resolution in performance mode makes a huge difference as well)
It's all a bit counter productive. Upscale to 4K yet lose fine detail in the process. That what you want to see more clearly, gets removed by TAA. I'm wondering if FSR can do a better yet at preserving fine detail without introducing shimmer in motion.