To be honest I don't know how feasable this is, but wouldn't it be awesome to be able to host/join PvP sessions (or PvE for that matter).
The hoster(s) select map, type of game, rules, password, etc. and people get a set list of hosted games to join. Basic stuff.
I remember the fond days of unreal tournament where at the end of each game the next map with the same players loaded instantly. That would be awesome in FFXIV! How right am I?