A few years back there was one Late War Arena, then at a certain time every evening it closed and it went to two LWAs. It was a hassle but very livable. You would typically log in several times, see that one Arena was full, go to the other. It wasn't ideal, though it worked.
The reason AH went away from that arrangement was numbers. When the bewitching hour happened, and the one large Arena closed, 100+ would consistently not log into two arenas.
I only mention that in response to those worried about the automatic side balancing, resulting in multiple log-ins. With automatic balancing, remove the "12 hour" rule and ENY/Perks I say give it a shot. I agree with the Snailman, the current three-side war isn't working so well.
Dear AH, times have changed and what didn't work well a decade ago may improve the model today.