This is a mess of an article. The M4A1 spec rifles will continue in 5.56, specifically the M885A1 Enhanced Performance Round. Upgrading 480,000 of them seems like a smart move, if the CQB packages and optics make them more effective in a changing battlefield environment. None of it appears to have anything to do with the new 6.8x51 Sig rifle, which is basically an AR-10 with a piston-based gas system and will (thus far) be produced in smaller numbers.
Thank you. I was totally confused by the article but I thought it must have been me...