Using lynx (or elinks, in my case) to view HTML email in mutt is the historical solution. I think the desire here is for a reversible transformation. E.g. I can receive an HTML email, view it as Markdown, reply using Markdown, and then send an HTML email in reply.
Unfortunately, I think foreign email clients would mangle the HTML just enough to stop this from working. You'd have to start implementing a tag soup type parser to coax incoming mail into something intelligible.
Re:Mutt 1.7.0 released
by dredmorbius on Sunday August 21, 2016 @06:04AM
(#12330246)
We're almost at that stage with HTML already.
I'm thinking that a multi-pass parser:
1. Is this sane HTML5 markup? I'll eat that.
2. Is this a borked-but-manageable variant? Strip the cruft.
3. Is this Beyond All Hope? Just dump it as ASCII. It'll be blockquoted in reply.
HTML is no longer a peresistent, stable, or universal interchange format.
For complex HTML to plain text try https://www.google.com/search?q=lynx+convert+html+text .. most text browsers can do a reasonable job of it.