As I stated, the "standard" knuckle coupler is useless.

…useless for automatic coupling and uncoupling of any kind of line (air, electric, control). Also, because of the fact that all couplable units are self-contained, the longitudinal force between those units is pretty small.

The "standard" knuckle coupler was never intended to do anything beyond transmitting longitudnal forces.

Considering "good practice", Caltrain may have one or two rescue trains on standby, and those rescue trains will have a coupler adapter (I can imagine a metal piece fitting over the "standard" knuckle coupler and allowing mechanical connection. And, as the KISS has two or three completely independent drive trains, it takes quite a bit to prevent it from limping on its own power to a workshop.