Hello!
We've upgraded the Dungeon joining experience to include a queue when we're at maximum capacity.
First, party members will now get notifications of what their party leader is doing.
Second, while in the queue, all party members will have their sidebar show information about the queue status.
Third, once your party is ready, the party leader will get a queue 'pop' notification.
Keep in mind this queue system will only kick in when there's not enough room for all players to play.
Since we added a lot of SkyBlock servers, there's usually enough capacity for everyone at all times of day.
You will probably see it in action once Catacombs - Floor 4 releases!
Enjoy.