It's interesting Jim, funny old world, we go from fully fledged battle rifles, to the intermediate cartridge and turn full circle back to battle rifles!
I guess America drums the beat in NATO and we all slowly fall behind and get into step... It's fair enough, they spend enough money to guarantee and effectively underwrite the rest of NATO's security after all.
I would hope the UKjust buys the rifle off the shelf from Uncle Sam and converts to the new calibre as it becomes widely available.
It appears Sig have won the whole shooting match in the US, from new service pistol, to new rifle and LMG and designed the new 6.8 round too!