Suggestions and ideas for increasing interest in previous PvP content

[Zojha]

They would have to remove the ability to choose the map played.

I dunno. WoW managed to keep multiple battlegrounds over several levels populated, even when they were still only server internal (and faction restricted to boot).

In the end, it's all about population. If you could pick any frontline and expect a match within reasonable time, people would just pick the one they prefer to play. But since the population is way too small for that to work, everyone flocks to the one people expect to have the best chances of a pop, typically the newest.