As far as I know (and I certainly don't know everything), all of the new proposed assault rifles for the US military are still sticking to 5.52mm 7.62mm NATO rounds; even the H&K XM-8, the Alliant Techsystems XM-29 OICW, and the still-born Fabrique Nationale SCAR, were all developed in 5.52 and/or 7.62mm.