Again....2012 NDAA did not EXPRESSLY authorize indefinite detention. It IMPLICITLY did by removing the restriction from use against citizens in one section that it EXPLICITLY restricted in another section. By rules of statutory construction, one could IMPLY that Congress intended US Citizens to be targets by their OMISSION.
So the amendment is meaningful and does repeal 2012 NDAA but of course it could be better. It opens the door for future EXPRESS acts of Congress to re-instate Indefinite Detention of Citizens. Another question that will probably be litigated is whether a purposeful omission from a statute can still be considered "explicit".