I would be willing to pay gems to increase the stack limits for materials in my bank. The current limit is 250, which I surpass with infrequently-used materials that I am holding until I have a character that can use them. (I also save some for guildies.)
I leave it to ANet to set the price (although I think it serves a similar function to adding a bank tab and could be priced comparably).
Signed: Another Hoarder
John Smith: “you should kill monsters, because killing monsters is awesome.”