Genbuckets for cheap as
x o n e said, maybe add sand genbuckets for an expensive price?
Make the custom enchants on gear reduced, so people don't just grind and hide in their bases.
Make crapples a little more op so they actually regenerate your health when getting crit out by 5 people.
Make sure that spawners aren't able to watered (like sponge).
Make sure cannoning is very very good.
I would like /f fly which could cost like 20m (maybe more) for the faction to unlock, or it could be dependent on the faction's value. But only fly allowed in claims.
Allow printer for base work etc.
Make sure obsidian isn't able to be destroyed by a creeper egg, therefore glitching won't be as common.
Add /sell hand therefore people wouldn't lose motivation to sell farms.
Make sure TNT isn't too cheap therefore raids aren't ez pz and cheap.
It would be good if a factions is somehow only able to mine a minimum of 5 blazes in the nether when it resets so some factions don't get to op by getting all the blazes and meaning smaller factions won't be able to get any.