There’s one banking idea I’ve come across a couple of times in fiction and immediately thought ‘Why is this not already a thing?’; The ability to define rules for how to handle incoming deposits.
One of the simplest examples would be defining a percentage of each deposit that should be ‘set aside’. e.g. for each deposit 10% should go into account A and the other 90% into account B. Other examples would be splitting the deposit at a defined amount, so that the first $X of a deposit goes to account A and any remainder goes to account B, having deposits that are larger than $X go into account A and smaller than $X that go into account B, or having deposits from certain people/sources go into different accounts.
This could either be an optional extra to handle deposits on an existing transaction account, or possibly a completely separate ‘drop’ account, which would only accept deposits and apply the defined rules to re-route the money to it’s final destinations.