One of the perennial problems game designers face is the tension between the requirements of fun PVE and PVP games. PVE thrives on variety (it's rather boring if the only difference between mages and warlocks is the colour of the light that comes from their fingers), whereas PVP thrives on homogeneity (or at least there's less whinging on the forums about how it's not fair that warlocks have fear but mages don't).
As a result, designers find themselves subject to a never-ending series of complaints. Improve things for PVP and the PVEers complain and vice versa.
Of course there is a simple solution to this: take the Darkfall route and simply design your game around one audience and let the others go hang. The trouble with this is that it isn't necessarily compatible with the mass market, as many people enjoy both aspects of the game.
So, what's to be done? Well, one solution is to simply have two versions of the game, each optimised for a different audience. For many games, this is unworkable, as the player base is too small to support it. For WOW, however, it's a different story. Fork it into eWOW and pWOW and Blizzard would have the top two MMOs, potentially with a more loyal player base, as it would be easier to make changes to meet the needs of the two communities. The eWOW rules would apply on what are currently PVE servers and the pWOW ones on PVP servers.