The quest mode (the more challenge mode after you finish the SP) which give you rare item, but can't be repeated again. Idea is allow a Monthly (or even a weekly) reset of the Quest. Could also add a constrain, (say only give it to the Club people). A flip variation is to add more quest, but you have a "Quest of the Week" type that change weekly. (ex. all Warrior Team for all maps).
Huh, I believe that's actually a new idea! And not a bad one at that. A monthly quest reset wouldn't detract anything from the game, apart from offering a second chance at rare hunting - which shouldn't be game breaking. People like doing the quests, and like having beat them - so as long as there's a differentiation (at least visually) from beating it for the first time, and beating a refreshed this could be good for sp longevity.
I've seen the idea come up semi-regularly, usually tucked away in threads like this one. It seems reasonably popular, although there were some interesting counter-arguments if I recall. Anyone who really likes the quests seem to realize at one point or another that they only get to do them once, and it's kind of effecting how or when they approach the idea of buying club membership. It's interesting to think that if you really like them, they're something you can't ever do again even if you just wanted to simulate the experience for added challenge.