Syncaine of Hardcore Casual has a good post with excellent discussion on the subject of whether you can have a game with good PvE AND good PvP. Syncaine has a long list of games which either had good PvE and bad PvP, or the other way round. The only exception being games that are bad at both. :) But can we have a game in which both PvE and PvP are good? For the sake of the PvP-fans I would sure hope so, because games with bad PvE will be very limited in how many subscribers they can attract. If your first month in Warhammer Online, where you level up in PvE, is not fun, there won't be many people left in the second month to actually try the presumably great PvP part. The only alternative to having good PvE would be to give people the possibility to skip PvE altogether, like Guild Wars does, or the new WoW e-sports arena servers. Forcing people through bad PvE to reach the good PvP endgame isn't going to work.
As myself I'm not the biggest fan of PvP, I very much hope that WAR has good PvE, at least for the leveling part. I can live without a PvE raid endgame. But I certainly would want that leveling up various races and classes in WAR should be fun, and offer lots of different ways to play and different quests.
Of course there are dangers. If you want to have both fun PvE and fun PvP with the same character, the characters need to be balanced well for both activities. I certainly don't want to see a repeat of the WoW problem that for one activity you need a different class or build than for another activity. You just don't want a class in the game which is a must-have for PvP, but which is gimped for PvE. Or a class like the WoW tank with tons of abilities for PvE aggro management, which then do absolutely nothing in PvP. Apparently in WAR a warriors taunt will actually have an effect in PvP, great!
I think it isn't impossible to have both good PvE and good PvP. But it might be impossible to have both a PvE and a PvP endgame. I see a big divide between games which have the PvE leveling game end in a PvE raid endgame, and those where the PvE leveling leads to a PvP endgame. If you try to have both, you get DAoC's Trials of Atlantis disaster: People forced to play endless repetitive endgame PvE content to remain competitive in PvP. DAoC had to introduce ToA-free extra servers to keep people in the game, because everyone hated that system so much.
So I'm looking forward to the dark world of Warhammer Online, with a very different type of story. I'm looking forward to level up various classes and races. I'm looking forward to PvE innovations like the tome of knowledge or public quests. I might try a bit of PvP, but that won't be why I'll be playing. So if PvE in WAR is bad, I'll be back to WoW pretty fast. And I'll take my millions of casual carebear friends with me. (Not that I have any influence on them, I just tend to think along similar lines as they do). And I think EA, being the maker of The Sims, has enough internal knowledge as to where the money is, and enough influence over EA Mythic as to force them to go after that money to make sure that WAR will at least *try* to have great PvE. Anything else would be financial suicide.