pvp can be great fun but balancing issues usually start killing the fun.

Its hard to have good, nice, fun and defined pve classes and on the other hand they have to be kinda "equal" in a lot of ways to have similar chances. PVP heavy games are full of balancing flamewars.. and usually the nerv-fest starts on dev site to get the pvp whining under control.

I don't mind it in controlled areas like you posted though. A good way to balance things for pvp is nerving stats for PVP only. But most games do the all over -nerv and this affects good pve... So i hope if it gets implemented, it doesnt affect pve.