Based on experiences of difficulty in getting groups for Comic Book Series, I believe that a queue option would improve quality of life for players. It can be a real pain soloing those suckers, often leading to folks getting stuck on a specific boss. I would suggest a feature similar to alerts where players would temporarily level up based on the group in the instance. e.g. level 11-20 would be raised to level 20. Increments of ten levels would allow folks to potentially use some of the items that drop from mobs in the instance as well.
To go further, I would also suggest the ability for players in an instance to also be able to fill out their ranks should members leave unexpectedly. This cuts down on frustration in games such as World of ******** and would increase flow in gameplay. Allow a button for the group leader to allow this function, perhaps even requests for specific roles for the incoming team members. This is a simple function, but will improve quality of life for players substantially, especially due to those long waits for specific instances.