I'm always running out of shared bank space and bank space so I think it would be really great to have a bank elixir that permanently increases your bank and shared bank space. Or make it a member benefit considering there is already an inventory increase for members.
This is a very good suggestion and idea. We can already increase what's in our house by using an elixir; so why not have an elixir that increases what our banks and backpacks can store too.
I really like this idea, because even with sell, feeding my pets, and out right destroying items, I'm usually at max in my bank, backpack and shared bank. And even if these elixirs weren't available to the general public, they could be available only to members. And when other players asked how did you increase your bank, backpack and shared bank's storage sizes; you can proudly tell them; its cause you're a member!