Hi Sedy,
People have suggested increasing invo space for a while now, and people also have a problem managing hot key slots due to pots/trans etc.
How about an extra invo bag that would open using a different hotkey instead of 'I'. This would allow people to put the bag at the side and use it as trans storage etc to free hotkeys. So you would get double usage i.e. extra bag of storage + extra hotkeys.
Bonus points if that invo bag is the size of a guild warehouse ^_~
Maybe something sold for a lot of tears?

I think people would be willing to pay, and it would give people a reason to hoard tears.