I agree, perhaps a further version of the signal protocol could implement a definitive solution that better addresses this kind of scenario the way HSTS did for

I agree, perhaps a further version of the signal protocol could implement a definitive solution that better addresses this kind of scenario the way HSTS did for ssl certs. And combined with a friendly UI solution (like the new padlock | Secure string in chrome) would lead to easier detection of possible eavesdroppers by the lay person.