standards exist from ITU, GSM and IETF
ITU has X.400, X.500 and X.503. These provide a secure email, directory services and Authentication and authenticity. Except for certs, these aren't mainstream, if they were, there would be a compatible, integrated persistent chat standard, I'm sure. These standards anticipated the need for global directory (today we use LinkedIn) and means to prevent phishing and spam. Sad the standards didn't catch on.
GSM created IP Multimedia Subsystem (IMS), then Rich Communication Services (RCS, "joyn"), another open de jure standard. Would have an integrated, compatible persistent chat standard, I'm sure. Would have integrated Twitter capabilities into SMS. Sad the open standard didn't catch on.
IETF has XMPP. Sad the open standard didn't catch on.
The other challenge will be these networks cost money to run, but today they are "free" (no cost) to users, so getting users to pay won't be easy.
Most communicate via mobiles, and most mobiles are replaced every 2 years. If regulators insisted on open, standard support in smartphones, we could have ubiquitous support by 2020. Never gonna happen :(
In the 1990s, Sun bought then sold Cobalt Qube appliances; think Google Suite|Office 365 in a box (but much more primitive). I think the concept still has merit.
Can you put all these together?
If my broadband router's Ethernet ports supported Power over Ethernet, and I could add something like Raspberry Pi 3 Model B+, which ran as an appliance, (ran an open, self-updating OS and email, chat, etc servers; like Cobalt Qube running X400|X.500|XMPP) as part of an open global federation (like Diaspora), that might be part of a long term solution. In exchange for hosting the federation, it would be free for me to use.