PVP, could in theory improve fairly quickly, IF they can do monthly balancing patches. It probably won't be anywhere near perfect for a long time, but I'll take improvement in the mean-time.
For example, in regards to Sleep being over powered. Well in theory something like that can be taken care of simply by either reducing the duration, or by dramatically increasing the cast-time. That's not a major change, and since PVP doesn't affect anything else in the game it should be fairly easy to implement.
Will a couple simple changes like that fix things? No, probably not, I imagine another balancing issue would pop up afterward. If they're making those sorts of changes on a monthly basis though, the experience should steadily improve.
I'm not really worried about people not participating though. The PVP items are too attractive in certain regards, and there'll probably be a number of people willing to put up with unbalanced PVP to get them. The real question, is if they can improve it fast enough, and dramatically enough, to appeal to a wider portion of the game audience in general.
I think it's certainly possible for them to do that. They just, have to listen to player feedback, and implement changes in a timely manner, even if they're only subtle adjustments.
Edit: I realize a lot of my posts may sound like I'm going out of my way to defend the game, and in a certain respect that is true. I have a bit of a, devil's advocate impulse, and often times in places like videogame forums, that ends up turning into automatic defense of the publisher/developer. In most cases, I actually agree with most of the complaints being made, but it's hard for me not try inserting a bit of equal time into these sorts of things.