I think the best analogy here might be WHATWG and HTML5. Instead of creating an entire new and expanded 'second system' (as the W3C was trying to do with XHTML), the existing major players in that field created something that was a much more strictly defined standard that was carefully to be forwards and backwards compatible with the existing mess, with well-defined behaviour for non-conformant content, and then started building on that new standard.
The big players in email are now in the same situation as the big browser vendors. If they defined a strict subset of the existing body of de-facto email standards, critically with well-defined behaviour for non-conformant content, and then blessed that as email 2.0, they would then have something well-defined and workable to build on.
This might include mandating a restricted subset of HTML5 for HTML content, a canonical transformation of that content to plain text for interoperability, mandating plain-text email as acceptable (perhaps with a canonical transformation to HTML) the use of SPF, DKIM etc with specified defaults, SMTP with specified features enabled, etc, etc.
Then what is effetively a well-defined profile of traditional email becomes the new (forwards and largely backwards) well-defined email system, and we can all move forward from there.
But to do that, there would need to be the will to create an email equivalent of WHATWG.
The big players in email are now in the same situation as the big browser vendors. If they defined a strict subset of the existing body of de-facto email standards, critically with well-defined behaviour for non-conformant content, and then blessed that as email 2.0, they would then have something well-defined and workable to build on.
This might include mandating a restricted subset of HTML5 for HTML content, a canonical transformation of that content to plain text for interoperability, mandating plain-text email as acceptable (perhaps with a canonical transformation to HTML) the use of SPF, DKIM etc with specified defaults, SMTP with specified features enabled, etc, etc.
Then what is effetively a well-defined profile of traditional email becomes the new (forwards and largely backwards) well-defined email system, and we can all move forward from there.
But to do that, there would need to be the will to create an email equivalent of WHATWG.