I've always liked DC Universe Online's twist on the classic tank-healer-DPS trinity that defines most MMORPG's group roles. DCUO gives everyone access to two roles—DPS and then either tank, healer, or control (CC and power-restoration), based on their power selection—and lets them swap between them whenever they want.
It's a hybrid system that lets players specialize, while limiting the usual problem of there being too few healers or tanks because most people want to be able to level and solo efficiently. As a result, the queue times in DCUO are much shorter than they are in many other MMOs. And with the Role-Optional Alerts SOE's adding in the game's next update , which use specialized buffs to make any combination of players an effective group, players should be able to form groups almost instantly.
When the tool puts together a group of players, it analyzes what key role(s) your group is missing, and grants the entire team a buff that helps shore up their weakness. Your group will still have to be organized however, as the buffs will only be effective when all four players are fighting together.
The game's Duos—which plant two characters in a more challenging version of a solo instance—already function off of a similar desire to get people playing together, regardless of their character type, and have been a huge success by all accounts.
In the same update, SOE is also adding Novice Raids, alternate versions of all existing raids with lower gear and difficulty requirements. Their goal is to allow everyone to experience the story arcs told inside the Batcave, Kahndaq, and the Fortress of Solitude, and to let players start raiding much quicker after hitting the level cap, if they want to. Novice Raids will award the same quality of gear that existing raids do, but reward less of it per run.