I think this sort of thing would be nice for replacing the Touch Bar on previous generation Macs with a row of changable keys.

I don't think it solves the problem of touch screens in cars though. The benefit of dedicated physical buttons in a car isn't just that they are physical. It's that you can use them without having to look at them. If you don't know what the button does (because it's changeable) then you can no longer simply use it without looking.

It's probably still better than a pure touch screen though.

This. I'd be pretty surprised if (among those here who drive their own car at least weekly) anyone takes their eyes off the road to press defrost, volume, next track, change fan speed, temperature etc

Honestly, I think this would be worse than Tesla's screen. The oft-repeated benefit of buttons is that they allow a kind-of muscle memory to build up - so you learn to change ccommonly-used settings without taking your eyes off the road.

In contrast, this would offer tiny screens, presumably in locations even more distant (considering the range of locations buttons appear in typical cars) from the windscreen than the Tesla screen is, and by switching their purpose, you create the neceessity to examine them before pressing?

That depends entirely on whether or not they automatically switch between functions, or if you can manually switch them (like bookmark functions).

Is the front defroster so significant a safety concern that it must always be possible to activate with one touch/press/turn?

If so, then Tesla would need to dedicate one such button to the front defroster regardless of menu state.

IMO, yes. Defrost behavior and timing is "serious business" in the car business.

Not only is it specifically discussed in the vehicle regulations (https://www.law.cornell.edu/cfr/text/49/571.103), it has specific SAE standards for testing (https://www.sae.org/standards/content/j381_202006/).

I don't know if any of them specifically require a certain number of presses or such - I've never had an "old style" knob climate system that would automatically turn the blower to max in the defrost position, though that certainly helps the process. But neither have I ever run into a vehicle where the functionality is actively hidden. Scan for the defrost logo, front and rear, interact with the proper controls. To remove this obvious behavior from a car randomly speaks to an insane level of disconnect between the designers (who mostly operate on the concept of change for the sake of change, because any change makes it look new) and users (who, generally, would rather things stay where they were).

I don't care if my car UI wins international design awards for Excellence in Minimalism (ExMn) or something. I care that I can use it to make the various systems do what I want, or put them in a sane "Automatic" mode that then does reasonable things with them. And, further, I very much do care that they don't randomly change on me between trips in the vehicle.

Someone linked the SAE standard in a different comment, but that and the law together basically say nothing about how to turn it on. It only says that you must have one, and how effectively it must perform when on. Then again, both of those are from the late 60s, when computers in cars were still unheard of, physical controls for everything were the norm, and perhaps common sense prevailed a little more...

I’m not up for buying an SAE standard today so I hope someone else is, or already has it, and can do so for the discussion’s sake :)

It’s pretty important. The windshield will sometimes fog up suddenly while driving. The driver needs to utilize extra care and pay more attention looking out a partially fogged windshield at the exact moment that they are forced to go through menus in a touch screen.

GM has a sort of neat solution in the new Hummer, a row of physical buttons/switches directly below the screen.

My car radio has this as well: I have dedicated volume knob with mute push, next and previous track buttons, and a Home button that takes the nav system to the Home Screen. It’s minimum, sufficient, and I would really regret not having them.

Some vehicles do have hard buttons overlayed on top of the screen.

The Range Rover evoque for example has a pushable wheel that sits on top of a screen (with a cutout in the center), so the part within the wheel will change based on the context.

I think that's a really good middle ground.