It depends on the regen capabilities of the car. My Bolt can regen at 70kw in Low (the one pedal driving mode).

With a 60 kw battery that is about 2% of the battery per minute. Or 1.2kw/minute and I get 3.7 mi/km, so about 4.3 miles of range a minute.

Have you by any chance tested regen by towing?

I'm assuming regen is designed to be used for short periods when slowing down, I wonder how long it can be used continuously.

Also, what would be the requirements for the towing vehicle? 70 kW of extra load is no joke, and car engines are generally not designed to handle heavy loads for extended periods of time.

The EV can handle it for a long time. I've never towed a vehicle like this, but I've gone down very steep mountains with nothing but heavy regen for over 45 minutes.

Some vehicles could maybe handle towing an extra 70kw (~100hp). You could always use a lesser regen level more suitable to the towing vehicle too.

Likely something less than a few miles.