Time to make a billion dollars on something else, then start up a car company designed to fail. No investors, design a car for a 60-70k buying price, few bells and whistles, but built to last indefinitely with basic maintenance. Start the company planning to practically close it down just after the last preorder customer has their car delivered and become a maintenance company with a few employees to make replacement parts and install them. If demand rises, redesign for the new times, ramp up and do it all again.
Who wants an infinite lifespan car anyway? Everything else would be getting safer and more fuel efficient. Might as well get around on horse and buggy.
For one most engines are pretty much at their peak efficiency, for two practical safety features reached peak between the mid 90s to the early 00s. Most modern safety features are ironically enough not all that safe, for example lane assist makes people pay less attention or it tries to assist in the lane and overcorrects. I see the latter rather frequently in my area since windy roads, usually the damned things are trying to avoid the white lines of the shoulder and overcorrect over the yellow.
I think modern safety standards alone would cost a few hundred million in research, or make it necessary to start from an existing donar car to make the type of thing I'm dreaming of.
I doubt a modern manufacturer would want to partner with a company designed to make basic but everlasting vehicles, so the imaginary billionaire would probably need to buy up whatever car the engineers want to start from in bulk.
Having worked on and had every major brand (and some obscure ones) in my family, there's a reason Japanese cars are considered the most durable.
We've driven numerous Toyotas and Hondas 300k+. Some we still have, 30 years old or more.
Working on Toyota and Honda is generally much easier and far less frequent than other brands.
You can see how American car companies enshittify things when there's a joint platform (Ford/Mazda, GM/Toyota, Chrysler/Mitsubishi). Invariably the American version is inferior, and even the Japanese company version often suffers with some of the same shitty design/engineering choices.
I refuse to ever again own an American vehicle, or even one of the joint platforms. I've had both - they suck to work on, require more frequent repairs, sometimes to things that just never fail on Japanese cars (especially electronics and control systems... Looking at *you" Jeep/Chrysler).