The problem is, you can hardly create a cap system that achieves all goals at once without pissing anyone off at a certain point.
We are looking for a system that
- prevents getting numbers in any single arena from getting too high, ("unhealthy") , whatever that number is (lets say, for discussion purposes only, 300)
- balances the load between the arenas, so that it's not hundreds of players having fun in one and a dozen boring themselves in the other
- is getting that balance as quick as possible.
The last two are the difficult ones to meet. Once you enable the cap, it takes time for the second arena to fill up. Unfortunately the current system is producing much grief for those flying at "early caps" time.
The only real "solution" I can think of would indeed be getting the caps into effect later than it currently uses to be, when more players are online - and then remove a appropriate number of players from LWO, so that both arenas will be up to the same numbers. For example: population in LWO gets to 300... zooooomg: LWO 150, LWB 150.
Of course it's not that easy... you can just randomly suddenly kick 50% of the players out of the arena. I'm not seriously proposing this

But... I'm just letting my thoughts flow... how about a regular, scheduled "shift" system?A daytime arena, and a "nighttime" arena, or non-prime and primetime or whatever.
Let's say the single daytime arena get's shut down at the same time each day (like 16:00 EST or whatever time is best). The whole process could be automated to happen at exact the same time each day and include early warnings at T-30, T-15, T-10, T-5 minutes. Then the arena closes, and the two "prime time" arenas will open up, with appropriate caps placed on them. Both would then will fill up more quickly.
Of course players would complain (we always do, don't we?). But as it's scheduled & automated, so it's reliably happening at the same time each day, no one would be surprised by a sudden shutdown. And it would just be a 15-30 minutes timespan in which action would die in the non-prime arena in expectation of the shutdown, and the two primetime arenas get back up to numbers and action - and note a 2 hour time of seeing LWB numbers climbing up from 20-100 players...