BMW did this in the 7 series and I think some 5 series. A row of buttons in the center console that you can choose what they do. Unlike old style "preset" buttons they have a sensor in them to detect your finger being on the button before pressing it, and then it shows at the top of the iDrive screen what that button is programmed to do. I thought that was quite an elegant way to fix the "can't remember what I made this one do" issue you get with programmable buttons.

I think all of them from the 2010's had this, at least my 3 series does.

You could place small e-ink displays on programmable buttons.

That might be pretty cool, but a complete nightmare for shared/rental cars.

The complexity of modern car interfaces--including those that use random buttons--is already a massive pain in rentals. At least for nav, things like CarPlay standardize to some degree. But I frequently find myself hunting for all sorts of things on a rental.