this tag button need to be combined with the right punch to perform the regular tag throw (throw the opponent and switch your controlling character), so it would be very inconvenient to use the right stick button as tag button.
and, most of the players will be playing this game with a joystick. there is not right/left stick button on regular joystick.
Well right now they never allowed us to choose the right stick. hopefully when the full game is released, we can get that extra spot so we wont have to sacrafice our layout. if not, i wont be playin tekken tag for long