As a short-term solution, I could render at 1440p and let the monitor upscale, but I'm pretty sure the image quality would suffer considerably. The general consensus is that downscaling 85% (about 1800p for the 4K example) combined with image sharpening produces minimal loss in image quality and results in a 20-30% performance boost compared to the native resolution. This is the difference between the 6800 and the 6900XT which is significant!!
It would be cool if there were driver support; such an option could be set in the game profile. Native support in the game engine would be the optimal solution, but it seems that Trixx users are more than satisfied with the ability to determine the trade off between frame rate and image quality on a much finer scale than by selecting default resolutions. Anyway, if Super Resolution is still a ways off, AMD please consider something like this!