In the long term, it's certainly an interesting window into the philosophy of the design team. The classic "bring the player, not the class" may, in fact, have been wrong all along, or rather, a better term might be "bring the mechanics, not the class." You are still expected to have certain mechanics for fights, the point now is that, instead of feeling you have to bring one certain class, you can now choose among a few other classes to get the buff or debuff you need. Or, as Ghostcrawler put it elsewhere: Classes and races are enforced. Roles are nebulous.
Of course, not every buff will be considered mandatory for every fight. For example, Bloodlust/Heroism is considered an optional buff, one that can be very helpful to a learning raid group, but optional.
Looking forward to the future, Ghostcrawler also dropped some hints about where the buff system may go in the future. He said that they are looking at the distribution of buffs, and whether one style of a buff may be more powerful than another due to slight differences, such as, for example, where one class gets it passively versus another class that must cast it. Divine Spirit is the example he gave of something that will probably be changed. In short, it sounds like we may want to expect a slight tweaking of the buff/debuff system in 3.1.
In addition, he said, they are strongly re-evaluating "gimmick" fights such as Razuvious to see if they unfairly require one certain class or spec. Overall, they don't expect class or spec stacking to be required in Ulduar, and if it is, they'll fix it.
One final thing that's interesting to point out is that Ghostcrawler has mentioned that PvE mana regen for some classes is probably overpowered and will likely get adjusted, although that is not something that will come in 3.1. Since Replenishment remains mandatory, it seems likely we can expect either a lot of monster mana drain mechanics in the 3.2 dungeon, or a nerf to personal mana regen mechanics for certain classes.
Patch 3.1 brings us Ulduar, dual specs, significant changes to all the classes, and more! We've got you covered from top to bottom with our Guide to Patch 3.1.