FWIW all modern cars are equipped with fairly sophisticated electrical systems. One of the more common failure modes is that an older vehicle develops an electrical fault which either can't be fixed or can't economically be fixed; the result is that the car goes off to the scrappies. This (presumably) reduces the average age of the vehicle fleet on the roads (which may or may not result in lower emissions....) but constitutes an appalling waste of resources.
I'm not convinced it's affected the average age that much, simply because the rise of electronics has coincided with other technology that's reduced the effect of corrosion and so on.
But just like with Di2, the problem with car electronics isn't that they're electronics, it's that they're proprietary and not designed to be serviceable. Back in the days when people were routinely setting points and adjusting carburettors, consumer electronics came with service manuals, and easily-replaceable discrete components were readily available. I remember dismantling a broken television at a formative age and discovering a slot on the inside of the case containing a full schematic with in-spec voltages and oscilloscope traces.
Technology has moved on, generally trading serviceability for low manufacturing cost and increased reliability, and today's electronics is harder to service without specialist tools and skills. But that's not the barrier that people tend to assume it is. The real problem is usually that the electronics is encased in glued-together plastic, specialist parts may not be commercially available (or only available in prohibitively large quantities) and you can forget about obtaining protocol specs (everything's a serial bus now!) or whatever to diagnose faults without having to resort to reverse-engineering techniques.
You see this in cars too, with hard-to-repair and largely cosmetic bodywork damage writing off otherwise functional cars. This does at least go some of the way to solving the proprietary parts problem.
Are there many 'Di2 -only' framesets? Would you buy one?
Closest thing is probably the mid-drive motor specific framesets. And if I wanted an e-bike I might, on the basis that with such a system the frame represents a relatively small part of the bike's cost.
The solution for bicycle electronics is for someone to come along and make an open system a selling point. Falco did this by not requiring a proprietary battery (you give the motor DC volts on a standard commercially available connector and it gets on with it). At some point someone will no doubt decide that they might sell a few more widgets (to the tinkerers, motor-de-restrictors, free software enthusiasts and the molsihers of unconventional cycles) if they make their groupset Arduino-compatible and hold the case together with screws.
But ultimately, proprietary electronics is no different to derailleurs/shifters with non-standard pull ratios.
