we are already supporting a triple of the supported polycount as original quake2 had it (or maybe even more). Our "problem" is, that we can't really work with pvs, but have to render the whole level the player is at. We are using the quake2world render engine where jdolan did a great job with - he's currently working on glsl shaders and neat little things - as soon as he is done with it i'm sure we will merge it into ufoai. but we will also provide a fallback for older hardware.