I think what has happened is that in many places the wording describing the secondary brake has changed. It is no longer required to be an emergency brake and frankly at least in US cars it has always been impractical to attempt that usage.
In most cases now a dual master cylinder is your emergency brake in effect.
YOU had a very good idea. It all depends on who you show the idea to.
It has been "rumored" that Howard Hughes father bought the design of the oil well drilling bit from an engineer in a bar for a few hundred dollars.
That bit is the source of income for everything that they did.