This is all very nice, but the fact that the article doesn't even _mention_ images or attachments shows how divorced it is from the reality of most people's email experience. I happily used emacs as my mail-reader from 1989 to about 2009 (first RMAIL mode, then VM). The increasing importance of non-text formats made it cumbersome, and I somewhat reluctantly switched to GMail. It's hard to imagine switching back now.
the only images i find are either from spammy adverts or tracking pixels. Normal people don't put images in emails. As for attachments, you can open them in their native programs just fine.
I am not sure of your definition of normal. ;-)
Part of my duties at work include help desk and maintenance of a few pieces of software. I get eMail with screen shots of error messages on a fairly regular basis.
(Personally, I have made my peace with HTML eMail, what I really dislike are those humongous email signatures with corporate logos and silly disclaimers that often dwarf the email body itself.)