I think we agree that Django’s EmailMessage makes working with html + text email more complicated than it needs to be. (And more complex than it is in many other frameworks/APIs.) And this matters because html + text has become a common—perhaps the most common—use case.
This proposal tries to target that specific issue by moving some of the boilerplate complexity Django currently imposes on all EmailMessage users into the EmailMessage implementation. I’ve deliberately kept the scope narrow.
Your thread on class-based email seems like a much larger scope, with broad goals that also include generating email from templates. I suspect it will take a longer discussion to reach consensus on that.
The two approaches are not at all mutually exclusive. But they are separate ideas, so I think it would be helpful to keep the threads separate.