, downsampling is nothing special, and setting the ScreenPercentage (you call it SSAA) is nothing different than downsampling as far as I know. Any game can do this, you can just force it in the driver. So you can be happy about downsampling support directly in UE4 (and I am too!) so the players of your game can just set it in the settings instead of through the driver, but the performance cost is so extremely high that no one will use it. I actually use a Screen Percentage of 75% as default setting in my game since the differences to 100% are not too high but performance is so much better than 100%.
So I also really hope for alternative methods of AA or improvements to Temporal AA, it’s really blurry. Try to disable all AA, then use the level editor of your game for 1 hour and then turn Temporal AA back on, then you will notice how blurry everything suddenly is. I did this yesterday because I has to disable AA for some stuff 