The way I see it, the fundamental problem is that the producers of these systems don't want them to talk freely to each other. Every vendor wants to control the conversation (and when you see someone calling their product a "platform", you know they want to control all the conversations in a given sector). E-mail is the lowest common denominator that works, because it happened in the age where computer technology was developed to coordinate, not to compete and control.

Conversations between systems is an easy problem, in the same way translating English to Mandarin is easy if both people are also fluent in Hindi - they can round-trip through the shared language. Systems designers can also negotiate a common protocol. It doesn't have to be automated, it can work just as well with some programmers continuously keeping the protocols up to date. The problem is, there's a strong business imperative to not do any of that.