I don't see why companies can't retro older cars. Mazda did a retro upgrade, but not wireless. If it has the hardware, why not program it and retro it? Sure maybe Uconnect 1 (if they had that numbering scheme) can't support it, but 3 or 4? I don't see how much wireless CarPlay can be that much more demanding than wired. Then again, they just want to sell you a new car.
For a lot of car companies, the calculation is, for every dozen (or some number of) customers who would like to upgrade the electronics and can't, there'll be one who is nudged into replacing their older car, and that's a big win for the company. And there's the cost of keeping yet more extra stuff in the their dealerships, and older hardware in cars may not be compatible or capable of being upgraded. In addition, car companies tend to have this snobbish, "no,
only we know best what our customers want, we've designed the
perfect dashboard", attitude, which is why some held out so long against CarPlay and similar for so long (while we suffered through their mediocre proprietary systems - my last car was very determined to present me with its own elaborate and mediocre voice menu system, wanting me to jump through many hoops to set up a phonebook in the car, rather than just being a conduit to let me talk to Siri - it was outdated thinking).
Sooner or later, some car company will figure out to put in an iPad-quality touchscreen in the dash, connected to a module under the dash that's designed from the start to be easily replaceable (with a nice box-shaped space with connections to power, antennas, speakers, the
touchscreen, and
the car's bus, and a well-defined protocol for what it can mess with), and then advertise it as a feature, that with their new system, you can come into the dealer and upgrade your "infotainment and control" system the same way you can get a new set of tires (with lesser prices for software upgrades and higher prices for swapping to a newer, more capable module - but it'd be plug-n-play for them to replace, rather than something that was hard-coded for a particular model/year). Presumably they can make a case for keeping the modules proprietary (or rigidly licensed) if it can use the car's bus to control other parts of the car (climate control and more). They'd need to be able to figure that they'd make more on selling a lot of upgrade modules every year than they'd lose on the handful of cars that a few people wouldn't be nudged into buying because of aging electronics in the current cars.
If one manufacturer does this, and achieves visible success with it, then others will folllow.