Would you rather have a 1080p@60fps PS4 game downscale to 900p@60fps or 1080p@45fps. I expect dropping resolution is going to be the best way to port down to Xbox One that's why DF gave that as the best solution.
From those two options 900p@60fps would probably be preferred.
But that would only be considering as if resolution and frame rate were the only performance impactors. On PC, just playing a game you are given a few options to mess around with the settings that affect performance. AA, V-sync, draw distance, quality of graphics, etc. Devs are able to do a lot more, in terms of changing performance.
If Oculus Rift were to be released with support for PS4 and Xbox One games,(It is actually a possibility, both sides displayed interest.) Whether it means anything or not, but if it were to happen 1080p@60fps would be preferred over graphics quality especially considering that games will look amazing.