New Army "Caliber Configuration Study"

[stanc]

The Gustav might have the range and excellent lethality, but one suspects that it is too large to be a decent replacement for the 7.62 MMG.

I quite agree. Not only because of size, but also a number of other factors.

I don't know of any serious proposals to replace the MMG with the CG. The CG has capabilities the MMG doesn't, but vice versa is also true.