Instead of building upwards, Warhammer Online has a chance to do something different -- something that works better. The reason I believe this to be true is because at its core WAR is about the RvR experience. In an endgame where players are fighting other players, you want to keep them together as best you can and adding more levels is counter-productive to that. So as a developer what will EA Mythic most likely do instead?
My guess is for horizontal game expansions (additional content without additional level grinding) in the form of brand new Scenarios, Trophies, Tomb of Knowledge entries, equipment, racial pairings, classes or ways to smash the snot out of each other that don't require ten more levels to be gained. With a focus on PvP that includes integrated PvE content throughout their game, EA Mythic has a chance to avoid the pitfall of only building upwards. They don't need to keep awarding experience for character levels when there are PvP levels (they don't inherently increase stats and instead give various other rewards) and guild levels to earn instead. Of course, guild levels get your guild all sorts of cool stuff that will help in all aspects of the game.
The point of horizontal expansions are that they should offer more to do for everyone involved (casual or hardcore) without forcing players to abandon most of the previous content -- which is another issue with vertical expansions. If there's a particular scenario or city raid you really loved doing, it won't be buried underneath levels once the first or second expansion comes out. That doesn't mean new content won't make older content less populated -- that's just inevitable.
World of Warcraft managed to largely create its own audience by making massively games easier to get into for a wide group of people. Where it has mostly failed, is at allowing new and old players from easily experiencing content together and thus increasing content longevity. So if Warhammer Online doesn't go crazy with new levels every expansion, it's possible that this weakness of WoW's can become a very contrastive strength for WAR. If there's one thing that will give WAR an extra edge it's something like this. It's not about beating WoW at it's own game -- you've got to invent your own, better game.
