It can be endless abilities if the designers want. To change what the X, rectangle, circle and square does can be done for instance by L1/L2 scrolling ability bar up, R1/R2 scrolling ability bar down. With various toggles like L1 and R1 toggling what the X, rectangle, circle and square will do (like weapon sets, or skill trees, or simply free-form similar to Diablo III). I personally think a toggle system feels least synthetic over time and it still, with just 2 toggles, give 8 additional actions with the basic 4 buttons. Do it with directional buttons, like for orders, emotes and such and it would be 8 additional such things as well (kind of like how old counterstrike sorted premade voice-commands in sub-menus). I really hope it won't be exactly like for instance Defiance with rather few (ONE) ability where that one can be used every minute or so (too much shooter, too little sci-fi, or space magic if you will).