I think the only solutions are mort strict then the one we have. I seriously doubt caps will go away. It mighht be interesting if caps where set by country, where each country would only have 33.33333333333333333333% of the population, and if one country had lower numbers, you could join. then again, HT would still have to set a total arena cap...so in a sense more strict.
You could be forced to join a particular arena....I don't see that going over very well.
given these options, it seems to me what we have is better. Even though at times you see an arena grossly over capped, I haven't noticed it to take very long for things to even out a bit. I also think people would be kinda peeved if all of a sudden they got a random boot from the server.
So what else is there to have some form of cap control in the arena? and don't say just do away with it, cause I don't think that is an option on the table.