This is what I would love for them to have. A wireless connection with a simple plug into the RV would be a slam dunk. Not really any additional hardware required on the Rivian depending on how the communication is done and hopefully hidden tow mounts. Put the Rivian in town mode and physically connect the RV to the truck and go.I don't have all the details or the electrical schematics, its could be a simple switched relay or a more complex variable transistor which could feed a portion of the current to battery, bleed off to resistors or capacitors, or open up and save nothing. My dads RV bus talks to his Jeep that he tows wirelessly for signaling brake lights and such, There would have to be some kind of communication between the two vehicles.
If you could monitor the car from your phone and turn off/on exhaust style breaking that would be brilliant.
Notification on the phone when the car was nearing full or setting the level to get to full.