I don't see how the design could be adapted to disc brakes. The majority of vehicles sold have drum brakes on the rear, probably close to the 90% figure the person in the video mentions. Furthermore, cars with disc brakes on the back often have a cheaper trim version equipped with drum brakes, so reverting these back to drum brakes would not be overly difficult - swap out the mechanical bits and adjust the brake bias.

I would be very surprised if 90% of vehicles use drum brakes on the rear wheels (at least in the US). Every car that myself, my parents, my wife, her parents, have ever owned (except for one) has had disk brakes on the rear wheels. While I know I'm using proof by anecdote, I'm just saying I would be very surprised if it were even the majority.

Unless your parents are very young, or exclusively drove sports cars their entire life, that's almost certainly not true. Front disc / rear drum was a standard design for a long time.

You're more likely to notice disc brakes -- they are more visible from outside the car and require slightly more frequent maintenance -- so you may not be able to think of many cars with rear drums.

> The majority of vehicles sold have drum brakes on the rear

The majority of OLD cars. Modern cars are switching to disk brakes all around. The best design is actually a hybrid brake - it has a drum brake in the middle used only for the emergency brake, and the outer edge is flat for the disk brake.