Every 10-15 years US Army starts a project for developing a future rifle intending to replace M-4. This started in the 80s itself when the M-4 was getting reliable sorting the initial issues. This circus continues for last 40 years and M-4 is still there. Begining from the 90s, Ar-15 rifles/parts are so much produced for the US civilian market, that it has reached unbeleivable levels of modularity. In addition, many foreign nations have adopted similar patterened rifles (in small/large numbers).
Moral of the story: Don't see too much in the NGSW programme unless some weapon is actually inducted. It may very well be dropped as many of its predecessors.