I would really like it if there were dungeons/gates were having a party to advance was obligatory (or really helpful) due to the mechanics.
To access these there would be a queue, or a similar system to create a party.
If this is not possible, these could anyways be implemented as alternative paths to normal progression in a dungeon, after a sign that tells you you need X party members to go that way. If implemented as alternative paths, there would be strong enemies and good loot in those paths.
Obligatory party: