A fellow raid leader and I were talking about the sudden lack of Shaman that Primogeniture has now found itself with. Two Shaman re-rolled Death Knights, one went to another server, and one disappeared without a trace. (I really hope the last one is okay... never heard from her again.) So while we may be looking for a few good Shaman (as well as some other healers), that's certainly not the point of this post.
One of the reasons that Shaman not being in our guild is sort of a bad thing is the loss of Heroism/Bloodlust. If I'm not mistaken, some of the melding of the classes and removal of stacked buffs was to get people to take who they want to a raid, and not who they need. Looks like a raid still "needs" a Shaman.
For that matter, it looks like there's still a few classes that are kind of a must have. Looking over at MMO-Champion's nifty tool, it kind of shows who can cover which buffs and debuffs. There's a couple that are slightly flawed, but let's take a look at them anyway.
The first item that is on their list that is only represented by one class (besides the aforementioned spell) is Blessing of Wisdom. With changes to potions, I'd say this is probably a must have. Every 30 seconds or so, that's probably another spell you can cast. So, pretty valuable stuff. Then again, the mana regen portion of Improved Water Elemental, depending on your mana pool, could probably easily be about the same amount of mana regen, just not something that is always on.
Wrath of Air Totem is the next one that is awesome for your caster group. You really should have one of these in your raid. Oh... wait. That's a Shaman again. Dang. Well, let's hope you have one.
Power Word: Fortitude is a Priest only spell, but can be slightly mitigated with Command Shout or Blood Pact. Probably still preferential to bring a Priest, but there's still these minor substitutes.
Then there's Mark of the Wild. Okay, we now need Druids. And then Blessing of Kings. I guess we'll have to take a Paladin with at least 1 point (preferable 5) in Protection spec.
So, there you have it. The only classes you now need are Druids, Shaman, and Paladins. Every other class is simply a filler.
(And in case you didn't get the tongue in cheek attitude, other classes are obviously needed, but maybe not as much as the 3 above.)