Make that a 7mm, with a bullet of about 140 grains, and I'll almost agree with you. Of course, the attachment for an underbarrel grenade launcher of the M203 PIP/GP 30 type [or something similar] should be high on the list, and I think I'd want to see some sort of commonality with the new Mark 48, Mod 0 machinegun the SEALS are drooling about [essentially a 5,56mm SAW in a 7,62x51mm NATO rechambering] maybe even to include an option for belt feed. But it appears a nice first-generation start.
It is my understanding that it will be the basis for the OICW weapon system, which will include a 20mm "smart" grenade launcher. Prior to that, the launcher will be a modular attachement.
The 7mm sounds like a good round, but I'm inexperienced with it. Perhaps if I knew more, I'd be able to form a more coherent opinion.
As for that machine gun, it looks quite a bit like the South African SS-77 GPMG. Noo problem, as it's one of the world's best designs. i hope they didn't change it too much.