But complexities of any new system aside, what is an example of a cashing in of an unneeded example in terms of an activity?
Examples for cashing in: payment for order flow (was recently banned in the EU). They litterally sold their trading data of retail clients for money.
Not sure how you think brokers make money, but they get kickbacks from market makers and fund providers, or simply higher spreads. No one works for free.
Payment for order: what data was sold (or do you mean the orders as data)?
You mean broker as in a pure broker, not broker-dealer?
What about policing algorithms, for example? Who'd do that and how?
Who provides liquidity? Just natural supply and demand?
Sorry, I thought you just had some idea about basic financial services.