Probably the main thing that comes to my mind for the cosplayers is a lack of a place to go to take a break / get water without going back to the room. And that can take quite awhile with the elevators. Of course many suits are fairly simple and breathable but there's quite a bunch of us with more heavy suits or large masks / heads that restrict airflow. And I don't like to de-head out in public locations for a break.
Having a little room with some chairs and fans would be good. It gets insanely hot. Could also have the room double as a little repair station as well.
This would allow for us to cosplay for longer periods of time.
This is my first anime con and it just struck me as odd, with as many cosplayers as there are, there wasn't really a place for them to get out of character for a break.