The first major feature that isn't going to make it into release are 4 of the 6 capital cities. Only the Empire / Chaos conflict will have their capital cities of Altdorf and the Inevitable City. The Dwarf / Greenskin and the High Elf / Dark Elf conflicts will have no capital cities. As you might have seen in the video podcast (YouTube link, the link on the official site was dead at the time of writing), the capital cities are the ultimate prize in the RvR conflict. For two thirds of the game, this final prize will be missing.
The other major thing that won't make it into release is class balance. Originally every one of the 6 races was about to have 4 classes: tank, melee dps, ranged dps, and support (healing). Now the melee dps classes for Dwarves and Greenskins, and the tanks for Dark elf and Empire have been removed. That leaves the dwarves / greenskin battle at least symmetrical, but in the other two pairs one side will have 4 classes against the other sides 3 classes. And if you were thinking of playing Dark Elf or Empire and like group PvE, you'll be left to wonder how to do that without a tank.
Personally I'm looking forward to WAR for its PvE content: Lots of new classes, new zones, public quests, the tome of knowledge, and so on. For me 4 classes less at release isn't a problem, as they'll probably be in by the time I played all the remaining 20 classes. But somebody who was looking forward to WAR for the RvR must be devastated. One side beating the other because they have classes the other side doesn't have access to? Ouch! You finally crush the enemy, get ready to plunder his city, and are stopped by an "under construction" sign? Where is the point?
One day a game company is going to find out how to produce quality games on time, without bugs or missing features, and they will do to the current crop of game companies then same as what Toyota did to the US/Euro car companies. Until then we'll have to buy the equivalent of a three-wheeled car from Mythic Entertainment, or the model announced for last year only coming out a year later from Blizzard, or the car whose motor mysteriously stops working once per hour from Funcom. No wonder nobody takes gamers seriously, we seem to be a bunch of masochists.