City of Heroes has made it this far with very few raids (Hamidon, Cathedral of Pain, Rikti mothership). They are adding another, the Behavioral Modification Facility, as part of the Incarnate alternate advancement system. This is currently under testing along with actual raid groups (“leagues”). Really old school raiders might be familiar with games where raids are just fights in which multiple groups are participating, with any link between the groups, raid UI, etc. City of Heroes has been run that way; everyone in the zone goes after the Hamidon. The next big update will have official raid mechanics as well as an event queuing system.
Of course, normal City of Heroes groups are eight characters, while other games have ten-character raids, so we are talking about really big fights here.