Tesla has a history of being somewhat hostile to third party repairs, so I worry there will be a long between-period when this becomes obviously needed, and when legislation and/or market forces create a third party ecosystem despite Tesla’s attitude.

Enter the signed parts requiring a factory diagnostic box with Tesla private keys a la iPhone parts and you're out of luck

Even with ICE cars there's been a long history of manufacturers attempting to lock out third-party repairs and modifications, yet there are plenty of companies who specialise in hacking around those limitations.

In the case of an electric car, which is simpler in a lot of ways, it seems more likely that parts will just be replaced with third-party compatible equivalents; which might naturally lead to a Ship of Theseus situation...

The difference had been that most cars did not have a direct connection to the manufacturer. Tesla has the ability to disable third-party parts and accessories remotely unless you prevent the vehicle from connecting.

This is already a thing on some newer Toyotas. For example, if you wanted to replace a FCW camera, you'll need to subscript to Toyota's service to get something signed so the replacement camera will work with your car. "ECU Security Key".

As someone who bought a used 2010 low mileage element. The touchscreen radio/gps is slow and uniquely terrible in a way I had forgotten 10 year old tech is.

It’s not heat but only radio/gps thankfully. Looking for a drop in replacement has been challenging as it’s not clear how one will work with the back up cam and steering wheel controls.

I’ve just started looking however