This probably is the solution - as cryptocurrency advocates like to say, "not your keys, not your coins", but for certain people an IOU from a bank saying that

This probably is the solution - as cryptocurrency advocates like to say, "not your keys, not your coins", but for certain people an IOU from a bank saying that the bank owes them some coins is preferable to having the actual coins and the benefits+risks associated with that. It's similar to stocks and bonds - you could own them yourself, but for not-huge private investment it's often simpler to have a financial institution hold them on your behalf.