I vaguely remember we had something like that a few years ago as a test run, shortly after the great split. The waiting queue - You could wait for a spot to open or switch to outnumbered side and enter arena... *sratchhead*
My idea would always give you at least one LW arena to enter at all times, no waiting, and you wouldn't have to change sides.
It would also mean that the arena you would be joining isn't one where you out # the nme.
Voila! Balanced sides.
(I know it can't be THIS easy... Help me find flaws here people...)