Are you confusing the degree symbol with the numero symbol? The degree symbol seems completely off-topic to me.
What I did was draw a clear distinction between formatting markup and glyphs. That’s a separation of duties that needs to be maintained: the Unicode consortium is the authority on codifying glyphs, but stays completely neutral on markup, similarly w3.org stays out defining new glyphs. See http://www.w3.org/International/questions/qa-chars-vs-markup.
I find I was wrong guessing that the numero symbol might be on a French AZERTY keyboard. The lack of one there suggests to me that No. is the best plain-text № , and that a sugar-free extension technique to beautifying that notation, and not using it as a justification for a sugary N^o^ notation, or similar.
Similarly if writing degree symbols really is your concern, a similar sugar-free extension approach could be used. But all of that has to do with better ways of writing well-defined glyphs, and nothing to do with superscripts.
If there’s well-accepted e-mail friendly notation for something, say x^2 for x2, then that (no trailing ^ delimiter) might be an interesting idea for an extension, but I don’t know of one for subscript, and I dislike the idea of using tilde for it without requiring some declaration of intent in documents doing so.