More than once, I've been in parties where the leader drops out and leadership is not transferred to another player. This always creates a problem, because if some players go offline or inactive, they can't be removed by anyone else.
Also, I know 8-10 players is a generous amount already, but 12-16 players would be very nice for dungeons if possible. I've been in a lot of parties that are full up already, when even more players roll in asking for invites. This is mostly an issue because two parties or more in a dungeon at one time is usually counter-productive and frustrating for everyone involved.
While I applaud the improvements that have been made to the party system over the years, these things should probably be changed so that people don't have to keep re-forming their parties to allow more people in.