I know, it's been suggested before. But now you can read my crappy version! I'll keep it short:
Randomly placed NPC somewhere in Haven that holds however much mist you give him, the mist he holds can't be used for anything other than transactions back to your mist energy meter. If your mist energy meter is full he can only take mist from you, not give.
Why is this balanced?
-Can't craft high level items with saved mist
-Can't use saved mist for complete gate runs (you'd have to return to Haven to get more)
-Can't start a guild with saved mist
-Can't unbind items with saved mist
-Would not affect any other mist/energy based things
Yes; I know the clockworks are supposed to be the bank that convert mist into more stable CR (and/or eventually CE), but traversing the clockworks takes time. Not every player can play every single day to maximize the CR he or she would gain and I think this would be a great solution for the majority of those players.
The ONLY way I can see this being even SLIGHTLY abusable would be if somebody saved up their mist and then got strings of consistent, lucky pubhops to the profitable part of a gate. But c'mon, really? REALLY!?
Sorry, but I think this is why OOO and Sega implemented this "Regen-able Mist" They wanted to encourage people to buy Crystal Energy, by the means of money, to help support the company and developers.
I can see this possibly, by a real low chance, seeing this happen in the future when the game makers are financially stable and making tons of money out of this...but I think for now, it's a wait situation at most.