I don’t see how that applies to be honest. The default has changed to html a long time ago and that’s what people expect.

What would be great would be if clients detected when I send an email with only text and just chose to format it as plaintext then BUT importantly, that th e reverse happens in the reading client: it formats it the same regardless, so my text email doesn’t look strange. Needs to render with the same font etc.

it almost never happens that I send a plain text email though since my org like so many prescribes the use of an image as signature. Not to mention that 9 emails out of 10 contains other images anyway.