Kaplan does say that Blizzard thought the progression rate for Burning Crusade was done well, and that they are looking at getting even more players involved in endgame, which, with the coming of Zul'Aman and the lowering of the Heroic reputations, is something we've observed before. He says also that Blizzard is planning to involve reputation more with daily quests, while at the same time making sure it's not a grind (hopefully this will mean gaining reputation from daily quests like the new ones-- attaching instance runs or battleground fights to daily quests, with reputation as a reward). And finally, Kaplan hints at lore in Wrath of the Lich King, specifically saying that "Humans, Dwarves, Tauren, and Trolls will all have their storylines developed further" in Northrend.
Sounds fun. He doesn't give any indication of where they are in the development process for the expansion (he does work for Blizzard, after all), but it definitely does sound like Blizzard is hard at work hammering WotLK together.