Cataclysm is supposed to be all about ripping things asunder. The world destroyed by Deathwing's emergence and the tentative truce between Horde and Alliance rent beyond repair. Indeed, many of the major faction cities will be significantly tougher nuts to crack, with new walls, new guards, and leaders placed in more defensible positions (I always did wonder why Thrall stood so far away from his potential defenders in the auction house).
However, their ability sets are still fairly boring, and there are still no serious in-game rewards for killing them. Given that the storyline now gives players ample reason to go after them (we're at war again, after all), this strikes me as a little inconsistent and a little sad. I realize that Blizzard doesn't want world pvp in the cities to be so prevalent as to make them unwieldy, especially for low level players, but a long respawn timer could fix this (quests would need to be turned in to a regent in the meantime).
Spontaneous, open-world pvp, if properly controlled, is one of the things that makes the game fun and unpredictable, and gives it some legs. So long as low level players are still immune in their capital cities (unless they attack first) and so long as quest givers can't be killed (or at least respawn quickly and/or have an alternative, like a regent), the only real problem is a little more lag. And frankly, I don't think a little additional lag would be noticed in Stormwind or Orgrimmar.
C'mon, Blizz, give us all a reason to subscribe to the global defense channel again!