Figure out a way to do WoW-style "hard" and interactive group content, but in EQ-style uninstanced areas, thus combining the respective challenges. Like say, for example, the dungeon has an area just like the first boss of Halls of Valor that's full of respawning mobs to kill, and there's a rare spawn that when aggroed starts the Hymdall encounter. If you haven't cleared the whole area, the fight gets harder because you have to avoid aggroing the trash while dodging shit. In a modern MMO you'd probably have to semi-isolate the area once the rare is engaged to prevent straight up griefing, but other people in the dungeon at the camps closest to it should be able to see you fighting it in the distance, and if you wipe they should have the opportunity to try and clear down to there and kill it themselves before you can make it back.
The idea is to get the EQ sense of community by putting all the players in the same dungeon where they can interact, but avoid making the boredom of waiting for the spawn the entire challenge. In EQ, with few exceptions, if you could get down to the camp and actually clear it out, killing the rare spawn was utterly trivial. The only question at that point was whether all of you could stay online long enough until the rare actually spawned. Hell, you'd often have to wait your turn on a long list just to get into the camp. This was possible because you didn't actually have to be any good to kill the frenzied ghoul, the only challenge was breaking the camp. If the encounter was actually hard and interactive like WoW bosses are, you wouldn't be able to just put anyone on a list, because if they fuck up and stand in the fire, you're not killing it and now somebody else can come take it.
In this system, the rare spawns wouldn't need to be anywhere near as rare as they were in EQ, and it would add an actual consequence for failing. If you fuck up, you have to spend time clearing back down there, and if someone else killed it while you recovered, now you have to wait 30 mins to an hour to try again. If you've got a good reputation on your server, maybe everyone else leaves your camp alone if you fuck up and lets you keep trying. Maybe they'll even come help you kill it. Conversely, if everyone hates you they'll park right at the entrance to the area to make sure to steal it from you if you fuck it up.