There are 13 circuit courts full of judges, all with their own lifetime appointments. I believe the proposed idea is that the current supreme court could be made up of random, rotating judges on temporary assignments from the 13 circuit courts. Currently, the 9 justices oversee one or more of the 13 circuits. So, we could expand the court to match the 13 circuits, and then, as justices retire/die, their replacements are randomly assigned to terms of 18-24 months from the circuits they oversee. It would still meet the constitutional requirements for the supreme court, as it only requires that there is a supreme Court made up of appointed justices in good standing.
I’m sure it’s more complex than that, but those are the basics of the random appointments and rotating seated justices.