Re: Any kind of central "real world identity" system is RIPE for abuse. Period.
You don't necessarily need any new infrstructure or any other form of co-operation from ISPs. Check out Delta Chat: https://delta.chat/en/
This is an open source Android chat app built on top of the existing SMTP and IMAP protocols. Pretty compatible with E-mail clients and has end-to-end encryption, it can use your existing mail accounts / servers. Of course gmail works as well. You don't need anything apart from the Android app to start using it.