what do you think about having the possibility to rent some of your bank and/or characters inventory space.
i mean to buy space its lot expensive and if you dont use it, get some money back will be nice: this is the fundamental of investment and economy.
on the other side it will be also nice to have the possibility to rent a space instead of buy it, becouse you may need it for a short time.
this idea could be done on a montly fee of 10-50 pack space.