@Vibstronium After testing several different scenarios with Sim Update 5, I am fairly confident that the only limit in the older Xbox consoles would be the GPU now. On my older system, the CPU is now enough for at least 30 FPS in all situations at High settings, RAM usage does not go above 6GB, and disk swapping is effectively minimised which makes the experience a lot better on a system equipped with an HDD.
As such, I think the Xbox One (S) could have a preset of 720p30 at Low-Medium settings, and the Xbox One X (which has a better GPU than the Xbox Series S by the way) at 1080p30 Medium settings. xCloud streaming should be a better option overall, but if they decide to port the simulator to the Xbox One generation in the end, the overall experience could be just passable on the One (S) and very good on the One X.