This idea is obviously inspired from the original Dungeon Keeper series, but I think it would fit pretty well in the current gameplay: creature upkeep. Basically, every X number of turns, it's payday and the Keeper's creatures head to the treasury to collect some gold. Higher level creatures would require more upkeep. If you don't have enough gold, well, hey might leave, pick a fight, vandalise your dungeon, etc.
Why is this a good fit for KeeperRL? As far as I can tell, currently gold isn't useful other than to buy items on the black market. Upkeep would give a much greater incentive not only to mine gold, but to keep mining for it. Keeps the Imps busy, too! A limited amount of gold on the map would also introduce extra challenge and a limit on how long a game can last. No longer could you simply buff up your castle, train creatures up to level 10 and just wait for the enemies to come to you.
Mining is really fun but right now once your dungeon's all set up, there's no important reason to dig deeper and keep mining.
What do you think?
