> But it's 2024 now. There are vastly more tools that can deal with HTML email than those that can't. Like, I wouldn't be surprised if it's 4 orders of magnitude.

Is it? Whatsapp, Signal, Slack, Notion, ChatGTP, are amongst the apps I use daily - and used by many non-hacker daily, that's pretty much "text only". all support some (subset of) markdown, which is close to "plain text" than to "HTML" in editing and displaying.

What I am trying to say is not that email should use markdown, or that HTML-email is bad or good. What I am trying to say is that there's clear and obvious proof that, in 2024, there's a need and use for "plain text". Even in tools that overlap with what email does.