So, instead of having a match making system like wow, I suggest against that, I have a much more engaging suggestion that people will like, I believe.
Definitely have a standard looking for group system like the old game though as an alternative.
But here's my suggestion, have a big hangout area, kinda like a tavern in a fantasy game, a place that's fun to lounge in. But aside from social stuff to do and interact with in these places you can find in all major sections based on level, it will have tables or something you can sit at and start a group, and set filters if you want, and have people sit at your table and discuss what mission or if the game has task forces or something like it, and form groups that way. Then you could have the group leader set the mission, it auto marks it on the map, and everyone goes to that, or have someone mass teleport them, or perhaps incorporate a teleporter that can be used to fast travel to the mission.
This would make grouping easier, give players control of who they team with, and still have LFG function to fill if people abandon.