As I am also a lover of 4/3 devices (a hugely innovative compromise step forward when introduced, in my opinion) I simply wonder whether the sensor area of a 4/3 chip could be integrated into an iPhone. Then you could add the optics in a modular way, i.e. an adapter would allow the attachment of a conventional 4/3 lens (which are available in fascinatingly different focal lengths). If you don't want that, you can then use Apple's slide-on plate with Apple's standard lens.
Not going to happen. At least not with Apple.
1) Their design (and monetary) philosphy is to control everything, you are advocating the use of third party lenses. They aren't designing camera bases for Sigma lenses.
2) My full frame becomes difficult to handle with a large telephoto, can't imagine trying to strap my camera to one. I hear you 4/3 is not as big, but it's not small, and to compete with full frames...those ARE big.
3) Why not ask the opposite question, why doesn't Apple license their technology to Sony to put in their cameras? That would be a killer combo. Not going to happen. Apple wants to sell phones. Look at the problem they have getting CarPlay into cars, and thats a LOT bigger market than real cameras.
Yes credit to Apple for what they have accomplished, and yes they are going to continue to push the limits. But physics count and at some point even apple is going to be limited by their small size. Not to mention battery life. And one area you gloss over in comparing cell phones to real cameras software is the advances in autofocus, not comparable. And autofocus requires motors and motors takes power. There is a reason real cameras still have replaceable batteries.
All these factors are about quality versus convenience. Ever since the creation of MP3 with their lower sound quality, the average consumer has shown they are willing to sacrifice quality to put convenience first. And while my HomePods have some amazing software, and sound great for what they are, they just can't compete with my Klipsch floor standing speakers. Again, physics (and power). Apple is pushing convenience in a great way but they will not hit the quality you can get with a full frame camera in the hands of someone who knows how to use it. All these things are tools with limits.
BUT, and here is a big but, photography is also about the photographer. And a good photographer can indeed get great results from a phone.
Just my 2 cents. So who knows, might happen.