Are these so-called text-only emails truly text-only? As in zero HTML/CSS and purely ASCII? I suspect not.
What I do suspect is really going on is a revival -- and I'm showing my age here -- of the AOL version: an HTML-lite, little-to-no CSS that looks like it's text-only. And I've created a few of these lately myself for the same reason: They load super-fast, they don't look "sale-sy," and they're written in newspaper-style sentences (e.g. 1-2 sentence grafs, 20 words or less, etc), not bullet points and taglines (i.e. copywriting instead of technical writing).
Actually, I have not had much difficulty getting approval for any tool or technique at APUS -- generally speaking, I just had to show the VP or AVP how it works and explain what it can do to make our program better. @theAPUSemailguy