Depends on your definition of lightweight. Something that a soldier can carry or something thats mounted. The round seems a good choice but a bit light for 2000 yds.
If it's mounted, then I'm not sure why the weight is all that important, or why the .50 cal isn't good enough. So I'm going to assume man-portable.
I suppose I could see why SOCOM would want something like that, because they task-organize weapons as it is. I'm just not sure about the Marines, because it would seem that such a weapon would have to replace something else, but the 2000 meter accuracy requirement is just not something that's going to be relevant in a lot of tactical situations. They're calling it a "lightweight" MG, so it doesn't sound like it would be replacing the M2's carried by the heavy machine gun platoon of the battalion weapons company.
Sounds to me like it would be replacing the M240B 7.62 within the weapons platoon of rifle companies. That's a really nice gun and extremely reliable, if a bit heavy. I'm just not sure you can increase the size of the rounds, improve range, and decrease weight, all while maintaining reliability. To some extent, weight and reliability are connected.