I remember when Arc90 first unveiled Readability (now "Reader Mode" in several browsers), folks were ostensibly right on board. One Mozillian praised it enthusiastically on her blog. I pointed out that the problem Readability solved was directly attributable to the lack of empathy by web site operators for their visitors—choosing instead to prioritize the operator's "expression" over the visitors' needs and best interests. It should go without saying that the template for her own blog hardly let it stand as an example of a minimalist jewel of legibility.

I'm also surprised at how poorly Reader Mode fares with "pages" served as text/plain. Is there even a case to be made against text/plain documents being shown with Reader Mode enabled by default if the heuristics can give it a high enough confidence score (with an opt-out escape hatch back to tiny monospace black-on-white for whomever wants it)? Eventually, we could do the same for very simple HTML pages like those found on cr.yp.to or danluu.com. I'd wager we could eliminate a huge part of the "Website Obesity Crisis" if unstyled pages were attractive by default.

True plain text -- as opposed to something like Markdown or another "plain text markup" format -- is hard for a reader mode, because you're going to have to put some effort into deducing the structure of whatever document you're looking at and that could be highly idiosyncratic from author to author. I don't think that's necessarily a reason not to do it, of course, but I can imagine it's why it's not high priority -- reader mode is already having to deal with all the ways modern web sites have found to make HTML highly idiosyncratic.