Ray, if the US Army wants a new cartridge I can’t see them taking any notice of NATO. After all, they adopted the 5.56mm round at least 15 years before the rest of NATO.
The problem I think is for them to be able to justify the cost of changeover in terms of quantifiable benefits. Since the Army brass have been determinedly defending the 5.56mm as entirely adequate for its purpose (“all you have to do is shoot them twice rather than once…”) it’s going to be hard for them now to argue that it’s not good enough.
OTOH, the saving in weight of up to 50% achieved with the LSAT ammo does indeed make a quantifiable difference (especially for machine gunners) so IMO stands a better chance of adoption.