Not being able to scroll quickly while having the stylus in hand is very annoying. Yes, you could use the pad, but you have to get rid of that stylus in before. ;)
Supporting the X-option EmulateWheel would help out here. So you could set it to enable scrolling by holding a designated stylus button for e.g. 1sec and then scratching in the direction you want to scroll.
In this way horizontal scrolling would come at no cost. Without three buttons and easy scrolling efficient working without a mouse is not possible IMHO. So having these features would be reaallllly nice! :)