Especially if the truck can hand off its payload to a fully charged & waiting replacement cab.

If you have access to a fleet or don't need the same truck back, it becomes more of a baton relay than a marathon.

With the kind of infrastructure required for that, I can't help but think it would just be a lousy version of an electric railway. At least for long hauls with high throughput.

Isn't it the other way around? With drivers, you can fit the charging inside the already mandated breaks, while without driver, you have to introduce longer breaks to get enough charge.

Idle time of EV-rig per day (30min charge every 4 hours): ~11% Idle time of Non-EV-rig per day (5min refueling every 4 hours): ~2%

Sure, for short distance trips where loading/unloading takes as long as charging the EV-rig, it doesn't make a difference, but for longer hauls, the charging pauses of EV-rigs will severely cut into utilization of the fleet.