GB storage in bank vaults:
I propose an extension of banks to include the provision of vaults for storing Gold Bars : this is a logical development as banks at the time were not restricted to just handling coin, but would store bullion and jewels in what were the forerunners of 'safety deposit boxes'.
I think this can best be handled by not extending deposit limits per level, but by 'mix and match' coin and bar amounts : thus the customer can store, in a level 4 bank for example, either 10 million in coin, 10 million in Gold Bars or a mixture of the two : I propose the value of the GB's for this case is based on the current average price in Avonmora at time of deposit.
I feel, with the recent change in OLOD effect upon GB in warehouses, some form of safer storage should be made available for gold bars, given their high intrinsic value.
As for the banks, a value-based fee for handling gold bar deposits and withdrawals is not unreasonable.
To guard against manipulation and attempts to dodge transport, the bars should only be able to be withdrawn in the port of deposit : so, if they were in the players Regis warehouse when deposited, that's where they go back to on withdrawal.