For example - If a title had a very heavy simulation loop (say 20ms), is it desirable to render at a greater rate, say 90hz?
This would always a present head pose correct to the view, without being stalled on simulation.
Or does this result in discomfort for the player, and instead render and sim should stay in lockstep?
Oculus implements a feature called Asynchronous Time Warp, where if a new rendered simulation state is not available when it's time to present a new frame to the user, the previous rendering is re-projected using the latest head tracking information, to minimize the apparent judder.
This is not quite the scenario you describe, but it is a situation in which VR experts have found it's worthwhile to display an old simulation state from a new perspective - breaking the 1:1 match between simulation time and presentation time for better perceived responsiveness.
A similar logic may well apply to your case: try it and see if it improves your game.
Note that it's actually very common for games to run their simulation at a different rate than the rendering, and interpolate the result to get smooth gameplay even on frames intermediate between simulation steps. So I don't see reason to doubt this tactic could also be useful in VR.
