How do get the banks on board? Remember you only have the energy of a lightbulb between all of them and no way to pay them without incurring structural transaction fees of the sort the FA is claiming are solvable by this solution. Also remember the banks actively distrust each other and spend literally all day every day in every one of their businesses trying to beat each other in every possible legal/ethical way (and also sometimes some illegal/unethical ones). It seems somewhat implausible that out of the goodness of their collective hearts they will all decide to run your raspberry pi, play nice with one another and do the right thing.

Some problems are super easy to handwave away in theory but actually pretty difficult to solve in practise.