When I use MSAA, I get shimmering, but not when using temporal AA. I don’t get this in non VR either. My frame rate is around 50FPS.

It seems that this is due to do with things being rendered as a single pixel and being contrasted against adjacent pixels. This also being combined with micro head movement (or micro tracking instability) and the said pixel being rendered for one eye and not the other. Looking closely to screen door effect, it looks like the squares contain coloured water that washes between adjacent squares - maybe I am looking too closely.

I really need to use MSAA because Temporal AA makes the scene look blury (but only in VR).

So I’m thinking, one solution is to make sure the player sees mostly the foreground where everything is rendered to many pixels. So in my world that means lots of trees, very few sweeping views.

Have other people decided that this is the way to go?

I am not sure why this is happening in your case, but excessive values for colours that cause the bloom effect to kick in gave me this issue. All I did was clamp the colour in the material. Further, I also could disable the bloom effect and not have this problem. I only had this issue with the specular points.

Try to enable ‘Normal Curvature to Roughness’ flag in material properties.