Atlus Japan's Youtube channel showed off Persona 4 Arena Ultimax's online lobby and it looks absolutely terrific!
The lobby contains other chibi-style Persona characters playing in Persona 4 Arena arcade machines to represent players that are either in a middle of a match or waiting for someone to join theirs.
The lobby allows you to use preset phrases like in the last game along with special icons you can give to your Persona character. There is also a "P-Card" system that allows you to add players to your favorites list.