Originally Posted by
Thage
In all fairness, we do see some fairly large concentrations of them working with Dalaran under Vereesa and, later, Jaina. So there's enough of them to maintain a standing armed force. That being said, I'm also extremely ambivalent on high elves being playable.
This is a matter of 'how many death knights are there?" Their numbers are nebulous at best, but despite their large representation ingame, the lore treats them as a small, elite force, much like how the blood elves, despite being the most numerous Horde race in player counts, were supposedly just barely hanging on by a thread in-lore before your character broke the Scourge's stranglehold on the Ghostlands.
In addition, from what we've already seen, worgen death knights would be a bigger retcon than pandaren death knights would. Not only does the PC worgen DK come from Arugal's brood, he/she somehow recovered their intelligence and broke free of Arugal's influence, and so did another/others, and became a great, heroic adventurer who inspired their other ex-Son of Arugal buddy to join the Argent Dawn, and died in the Scourge invasion.
Compared to, an adventuring pandaren whose wanderlust kicked in, and they had a buddy tag along. These two handle themselves well enough to get into the Argent Dawn, and yours ends up dying in the pre-WotLK invasion. Again, the player character DK is established as being somewhat special, and quickly proves him/herself a cut above the rest of the nameless Death Knights.
I wouldn't mind nelf paladins, considering that the entire reason Delaryn goes to Light's Hope to train is so she can spread these teachings among her people. Lore crumb's there, all it's going to take is for it to catch on, which it may well if Teldrassil burning caused widespread disillusionment in Elune and they feel the Night Warrior ritual is going too far.