I think it would be insanely fun to have a vials-only arena. Toss a few knights into a room full of recharging vial pads. For PvP, let us chuck vials at each other until there's a winner. Or, for a fun PvE spin, take the same setup and have monsters siege you from all sides.
There was a PvE section of the Firestorm Citadel that was like this. It was awesome.