The problem is that, as soon as they implement that, people will avoid it like crazy...
I mean, just look at RoM and CoS. Even WGT and ICP...
Even high level guildies will avoid them like the plague simply because they are mechanic heavy and take a long time and coordination to be done.
Personally, I'd take some interesting mechanics over "one-shots for difficulty" anyday, but I believe the majority of players just doesn't like them.
Also, look at the latest dungeons: WGT and ICP for Imperial City, RoM and CoS for SotH. They are all doing exactly what you want: mechanics heavy, increasingly. I bet the next pair of dungeons will be even harder on that aspect.
Always the same place, same boss, same mechanic. The Dungeon is instanced, so it's preloaded. It really shouldn't be that hard to have a modlar built dungeon system that loads different states, bosses, mechanics to keep mixing things up?
It should be cool to have a randomly generated dungeon, with various boss mechanics. For example begin with a HM Warrior that calls a Possesed Manticora mid fight, continue with a Skinrai & Vashai type arena, but with 4 quarters instead of 2 halves, an ecounter with 3 Velidreths surrounded by 6 statues and finally a Rakkat with 3 Warden Dusk adds that oneshot players