One of the things I'm learning in my foray into Warhammer is that the non-instanced group portions of the game are much more fun than the solo-PVE or the instanced PVP scenarios. I'm sure these all work fine at the endgame, but they create a huge problem for the middle levels.
I did a /who survey of my first server selection, Badlands, to see what the population looked like at my peak gaming hours. Of Warhammer's 40 levels, only rank 40 returned "too many results to display". For any other number, there were more like 2-5 hits. In other words, at any given level, you might be able to form a SINGLE group of players within a level of yourself if you could get EVERYONE logged in to join up.
Basically, Warhammer may have enough level 40 players for its seven servers (only Iron Rock and Gorfang, the free trial servers, ever display above "low" population), but it only has enough players in the newbie zones to support 2-4 servers and only enough players in the middle half of the game for maybe a single server or two. Unfortunately, you cannot simply merge all the servers due to performance issues at the top level, which is where most of the players have ended up. Therefore, you have to leave the population in the middle levels unacceptably low and hope that players will take some other path - soloing and boring instances, if they ever happen - to the level cap.
This problem isn't unique to Warhammer, though it does hit that game harder due to its RVR focus. Both WoW and EQ2's group games really suffer from current model of soloing to the cap and then trying to figure out how to group. Again, though, there simply aren't enough players in the middle levels to support a full-time grouping requirement, so there HAS to be a soloing level path, which can't be onerous and tacked on since that is what the majority of players will be using.
The only solution that comes to mind is to go to Guild Wars style of instancing whole zones. Basically, everyone is logged into one server for the purposes of forming groups and whatnot, but the server would spawn as many copies of the actual content as are needed to support players in that level range (i.e. Warhammer really could have 4 T1 zones up, a single zone in T2-3, and 5-7 copies of T4). In some ways, Mythic has already taken the game in that direction, removing the non-instanced Fortresses from the endgame path and shift players towards instanced city sieges in their place.
The downside to this approach is that it kills the community aspect of small, closed servers. Then again, it would also wipe out the need to worry about what server you choose to play on, and it might just mean that pre-dominantly group-based games could become viable once again. Between servers, vertical progression, and grouping, something has to give. If we want to have a game like Warhammer, which thrives on groups, that really shouldn't be the aspect that gets kicked off.