Why change? There are countless billions of rounds in circulation and millions of standard magazines. 5.56 has proven reliability and lethality. Adopting some niche caliber doesn't seem practical for the military.
7.62 NATO wouldn’t be a niche caliber.
I heard some time ago that troops were questioning the lethality of 556, and there was a push to go 762 NATO, a widely-used round. However, the 762 rounds are heavier and fewer to the mag, so that may counter the hearsay.