Although there probably isn't really any concerted effort to "keep plain-text mediocre", it can sometimes seem that way.
As we've been told repeatedly, just because something has been done over and over again doesn't mean that there's a precedent for it.
Using spans of text as a general indicator of rich-text seems reasonable at first blush. But selected spans can also be copy/pasted (relocated), which is not stylistic at all. Spans of text can be selected to apply casing, which is often seen as non-stylistic. In applications such as BabelPad, spans of text can be converted to-and-from various forms of Unicode references and encodings. Spans of text can be transliterated, moved, or deleted. In short, selecting a span of text only means that the user is going to apply some kind of process to that span.
Avant-garde enthusiasts are on the leading edge by definition. That's why they're known as trend setters. Unicode exists because forward-looking people envisioned it and worked to make it happen. Regardless of one's perception of exuberance, Unicode turned out to be so much more than a fringe benefit.
