“There’s money to be made at NATO.”
This will not go well. The 7.62x39mm is notoriously fickle in the AR-15/M-16 due to the bullet shape, the same issues that 5.56mm have in AKs. The Israelis worked most of it out with the Galil but that’s an AK-style.
The whole purpose of the M-16 project was to develop a lighter rifle than the M-14. The 7.62x39mm ammo is already heavier than 5.56mm. They can make the rifle lighter but that would require materials not suited for cold (aka plastic) being used by soldiers that are used to much sturdier rifles (Mosin, AK).
Yes, that's why I think it's about money rather than reliability and interchangeability.
They are going with 5.56x39.
The Galil used the magazine of Eugene Stoner's Stoner 62. The copy is so so close that the magazines are interchangable between rifles.
It had been Stoner's intention to develop his AR-16 rifle design into a 7,62x39 M43 version, but instead he downsized it a bit, and it became the AR-18 instead. Produced in the US by Armalite, by Howa in Japan as the semiauto AR-180 and Sterling in England, in both full-auto and semi versions, you need only to look into the top of a British SA-80 or German G-36 to see just how influential the AR18 was. A few other designs share its square section sheetmetal receiver, dual driving springs on dual guide rods, and short-stroke gas piston gas system.