A version of it passed as part of Defense Authorization 2017 (search for "disinformation").
-- Why would that open the door for censorship by social media? --
I don't see that link either. As far as I can tell, social media, like the press, if free to propagandize freely, including restricing public participation to opinions it shares, or at most, some "authorized dissent" so as to create an illusion of being fair and open.
This bill orders and authorizes the government to propagandize abroad, and to study propaganda.
Anything introduced by Ted Lieu and his minions should never have seen the light of day. I wonder if Ryan slipped it in.