Don't we have this, already?
Didn't TextSecure already invent an open group-chat mechanism with proper end-to-end encryption? They're called Signal or something, now, I think. I'd check, but I left my phone at home, today.
Between TextSecure (for friends) and good ol' email (family, more friends, customers and suppliers) and issues on our GitLab server (hosted in-house), I'm flush with ways to communicate with anybody I'd care to contact. I also have a phone. And I think the printer can even send faxes.
I'm honestly not sure what else one needs. What do people actually *do* on Facebook? Play Farmville and poke people's walls? (Ewwww...!)