As you know if you read enough about banking, and as the intro points out, banks already invest your balance in risky stuff. Namely they lend it out to small businesses, homeowners, and others at substantial risk for default. There are mitigations like collateral and sometimes securitization, but the risk is real and there and has blown up countless times in the past.
Yes, the stock market can "blow up" too. But at least you're capturing the upside of the risk with this model. Even interest bearing checking accounts share an infinitesimally small fraction of the return the bank can make on your money.
I'm not saying this is for everyone. When I was younger I would routinely deplete my balance and I do not think this is a good setup for people in that position. But at a more advanced age people tend to start carrying significant balances in their checking as a matter of course, and I actually think there is some strong if slightly counterintuitive logic here in this idea.