What a coincidence! We happened to talk about raid design and results with Ghostcrawler and Mumper yesterday, and everyone looked back fondly on Ulduar, among others.
Yes, the same designers and artists who worked on Ulduar are still working on raids.
Here's the thing -- Ulduar is an example of a raid where lots of players got to enjoy the first few bosses, and very few players ever saw the last few. Yogg Saron and Algalon were among the least-killed bosses ever, and not because they were exceedingly difficult. Rather, clearing the dungeon all the way to Yogg took up a big chunk of a raiding week (and you only had an hour to kill Algalon), and the ability to extend raid lockouts came later in 3.2.0 (but extending raid lockouts means getting less loot overall). Raid Finder partially resolves the length-of-raid problem, so we can consider designing longer raids, but that's not always an easy call. Long raids mean longer development time, and while some players might be willing to wait, we understand why others might get impatient.
Of course, having multiple raids in a tier (like the combination of Bastion of Twilight and Blackwing Descent) has the advantage of giving players different environments to play in while potentially making scheduling and logistics easier.
Pushing a big red button for Mimiron was very cool, and again is fondly remembered. We have created something like 40 raid bosses since the creation of those encounters however, and we cant help but think that it would start to feel really gimmicky and forced if every raid encounter had its difficulty set by pushing a button, (or not killing adds, or changing the order you kill the bosses, or the other mechanics we used in Ulduar). We think Mimiron would feel less special if there were six more bosses in the game with big red buttons, and we’re just not sure the design space is there to have a near infinite variety of means by which players launch a heroic mode in game.
Nonetheless, because there are so many requests for those style mechanics, we are considering doing a few bosses with optional modes (in the same way Mimiron, Freya or Sartharion had them) in Mists of Pandaria.
The thing is, the op mentioned nothing about raid length. Just about interest and quality of the fights. Just more interesting fight mechanics with more than one possible outcome.
And hello, thing is, with quality and interest aka MORE mechanics, the fights are lengthened. They aren't so cut to the the chase, straightfoward.