There are a few commands that I personally think would be interesting features to add into the server.
/trash or /incinerate - Destroys an amount of an item. This would be useful in scenarios where a player is on the surface or underground with a full inventory and needs space to pick something up, but doesn't have lava to destroy whatever junk items they're carrying.
/extinguish - Extinguishes the player if they are on fire. For the purpose of keeping things fair, it will be inaccessible in arranged PVP areas, PVP plots in Towny (A or B), or Parkour. (if I missed something, feel free to add.)
Bring back the auction system! (if there was one. I forget.) - The auction system was a fun and often competitive way to buy items people were selling before, and it was also a way to earn extra money from items sold that way (in some cases). It should be noted that there should be an anti-snipe system as well (to prevent last-second bids) to keep things fair in that department as well.
Thank you for your consideration.
~FProS