For me an ideal raid endgame would start with a dungeon that is relatively easy, and then get progressively harder with each following dungeon. As a consequence, players and guilds would spread out, with the best players advancing fastest, and the least good progressing very slowly, and that mostly through the inevitable gear accumulation. And all these raid dungeons would remain as they are throughout the expansion.
Blizzard's idea in Cataclysm appears to be to have a "current" dungeon set which is rather hard, and then nerf that set of raid dungeons when the next set of raid dungeons is patched in. Unfortunately the earlier version of this concept in Wrath of the Lich King shows that this simply doesn't work: The earlier raid dungeons just stood empty when a new set became "current". Instead of having persistent dungeon difficulty and a progression through them, the "add new and nerf old" concept just makes the old content irrelevant. If your guild doesn't happen to have finished their progression through the old content EXACTLY at the moment of the next content patch, you're screwed. If you are too fast, you have to wait around. If you are too slow, the boss kill you were looking forward to just got nerfed into being trivial and not fun any more.
If Blizzard thinks that by patch 4.2 they can get both the bored hardcore and the frustrated average players back into the game with one stroke, I'm afraid they will be severely disappointed. Some people will doubtlessly enjoy the new Firelands "personal development" daily quests. But their raid progression strategy is a complete dud that ends up making nobody happy.