It really is amazing to me that anyone thinks it's reasonable policy to ban end-to-end encryption. For the sake of national security, I would want to strengthen the security of digital data, not weaken it.
Can't we have E2EE+G? (end-to-end encryption, plus government can see everything) Not saying this is a good idea, though.
Note that banning E2EE implies banning encrypted p2p communications entirely. E2EE is a concept that applies only to centralized comms providers where all messages go through a server.
Practically speaking, it's impossible to ban every encrypted protocol (TLS, SSH, ...). It's also (probably) impossible to ban IP communications that don't have an "approved server" participating.
However, comms providers / social networks to date at least manage, authenticate, and introduce users at the serverside. Fully distributed projects have problems with spam. So governments would have to ban comms providers from "allowing" their clients to talk to each other directly and not via the backend. That's a hefty technological restriction, which would block a wide range of protocols (webrtc/SIP, torrents, probably a bunch of other Very Important things I'm not thinking of right now).