Many larger trucks such as 2 tons, school buses, and motorhomes, use driveline brakes mounted behind the transmission, same as the TC brake.
I have a school bus that I use in my business, it has only the transmission brake. It holds much better than any rear wheel brake, because you have many more times holding power. In other words, the rear wheels have to spin the parking brake rotor or drum several times faster than the rotor or drum on the rear wheels, whatever the gear ratio is on that axle.
A lot of motorhomes don't have a park pawl in the tranny, they have an automatic brake built onto the back of the transmission. When you place the tranny into "Park," it automatically sets the brake. There are no other emergency or parking brakes.
It does make a difference if you are talking about emergency brakes, or parking brakes. I think emergency brakes are a mis-nomer. I've never owned a vehicle where the "emergency brake" did any good at road speeds. I can slam down on the pedal, and you just feel a slight drag. Parking brake is a better term.
Just thought I'd pass this along. The driveline brakes work well on the heavy duty trucks, so why not ours?
Casey