Arena is a very fun mode that could become competitive if certain features were implemented: Spectator slots, More Maps, A few new classes (1 or 2 that uses Necro/Summoning since no class uses those skills currently in arena.) The lobby browser could use a overhaul to show how many people are in the lobby, Turn Timer, Max Characters, Gametype, etc...
Also right now there is no way to change your starting position on the maps if you host the game. Along with that there is a bug that if you play a game with another person, if they quit out of the match and you return to the lobby their "Slot" that they occupied will be bugged out and you cannot put an AI in that slot nor can another person actually join your game because it considers that slot 'Null'.
I'm thinking about hosting Arena mode tournaments but the way it is implemented right now it would be very difficult to organize and stream the matches considering some maps can only have 2 players in them at once with no spectators!