For me, running has only two potential uses: At the beginning of the game (where I need to know if those blasted humans are coming out of the base and stealing my medkits), and after everything's dead on a level. The first case is rare enough that I don't mind needing to press the comma key before running, and in the second case the only bad thing holding down a key might result in (as opposed to running) is running over acid or lava, which if I'm likely to do will result in me taking individual steps anyway. With enemies around, individual steps just plain feel safer, and without, unless there's dangerous terrain I feel very free to hold down the keys even if it means spending extra turns bumping into walls. This is just me giving my two smallest units of monetary denomination, though; I think this would be a good addition. Perhaps a simple Shift combination would suffice.