You would no longer need high voltages at all. We only use those to cut down on those very transmission losses because we're trying to reduce the amount of current. So you can drop all of the step-up-step-down stuff. On the down side: a short is then practically unlimited in current.

Exactly the point.

We will still need some step-downs, because current density is limited. But we will need fewer of them, and they won't need the monumental cooling they have now.

Superconductors have a limit on the current they can carry before the superconducting phase breaks down. This might put similar limits on the voltages.

I agree that the nature of this is entirely different to transmission losses, but I don't expect 230V lines carrying tens of thousands of amps. This would probably require excessive amount of SC material.