Car reflections on the 'high' setting was a known FPS killer and subsequently optimised as part of the last update. It seems Sector3 achieved this by simply reducing the refresh rate of the reflections to a point where they look horribly choppy on the high setting. This was quite a crude 'optimisation' in my opinion. The result looks quite bad so I run on the 'low' setting. The car reflections setting needs options for both quality and refresh rate so that those running high-end systems can get a more satisfactory result.
3D grass? Not sure if there are plans for this. Grass textures look great but yeah, a bit flat.
Night racing & weather - not in the immediate plans as far as I'm aware, which is a shame. I think wet races should be a standard feature of all racing sims otherwise we're not making progress as a genre. Sadly for R3E (as with some of its competitors) the focus is on pumping-out new content rather than bolstering the base game with core features.
Depth of field - I think this is planned. Personally I would only use it in replays as DOF makes no sense in driving cams.