Applies to all models capable of towing, but particularly to the CyberTruck and Model X. Right now, the Model X has the wiring connections for installing a 3rd party brake controller for towing trailers with their own braking system. The brake controller is recommended for trailers over 1000 lbs. The best brake controllers activate the trailer brakes gradually based on accelerometers built into the units so it can match the towing vehicle. There is no reason why the Tesla couldn't perform this function itself since it has all the required information already available or it can be input in a screen field (small/medium/large trailer). The upcoming CyberTruck is essentially advertised to be very capable of towing (up to 14,000 lb), so it would make sense to build it into the vehicle.
Furthermore, I believe the Tesla should be smart enough to even adapt the vehicle and trailer braking for optimum performance (i.e. minimize the towing effect on braking observed by the driver). It could even potentially figure out the weight of the trailer by doing a "calibration" brake where it doesn't use the trailer's brakes and compares stopping distance to a baseline without a trailer.
Once the software has been updated for the functionality, for existing vehicles already produced, perhaps offer for sale a module that would plug in to the existing brake controller wiring receptacle to connect the appropriate leads. (applies to Model X, unsure about other models)