In Chrome, if you copy CSS-all-caps text to the clipboard, it is copied as uppercase.
Intriguingly, in Firefox, it is copied as the original (mixed case) source HTML text.
I do like the idea treating all-caps as a style, just like small caps. The problem, of course, is that it makes it kind of impossible to type within it, since there's no feedback as to when you're typing capital letters at the starts of sentences or not.