I've been thinking of a possible Guild Hall expansion (like the Training Hall) where any number of players can join in a small, rule-free zone (so competitions can have their own rulesets) and players can fight to the death. The area can be sealed off from the outside. Players can only revive after waiting a few seconds and officers can teleport any player outside of the PvP zone (for competitions involving disqualification, and players not following the competition rules.) There could be a room for each tier, much like the Training Hall.
Some uses I thought for this expansion:

• Guild-vs.-Guild combat outside of the LD environment
• Competitions within guilds for promotions
• One-on-one duels
• Small competitions with unique rulesets