The beauty of it lies in the fact that it's an American designed rifle built by a company founded by a Ukrainian immigrant in America using Russian developed ammunition to fight Russians. Gotta love it Good for them.
If you want to read a good book get a copy of "The Gun" by C.J. Chivers. It's a history of the AK-47.
Every country that had anything to do with Russia had at least one AK factory. There are literally
hundreds of millions of them that were built. A lot of these still travel around on the world arms trade circuit.
Having to switch rifles and calibers all at once would be a supply system nightmare. Having a rifle that uses current ammo, even if you do have to change mags, with the ability to switch to a future caliber by just changing the upper is good planning. You're able to stockpile ammo and uppers for the change without interrupting your current supply.