The problem with this suggestion is that you're asking for a zone. An entire zone. One pvp zone is one too many. The resources that it would take to build an entirely new zone just for pvp are resources that I'd rather see go to something else. Is that a selfish thing to say? Maybe, but a pvp zone is a big enough deal that it'd have to be THE big feature for a patch, kind of like how the potd was the big new thing a while ago and eureka's going to be the big thing in 4.2. That patch would end up being pretty dry for everyone who doesn't care for pvp.

If I'm being honest, I think too many resources are being spent on pvp in this game as it is. There are other games that are much better suited to it, it's really not something that needs to be dragged into this one.