One requirement I have for any proposal is that the effort required by an author to comply is minimal.  Part of the reason that the SRFI process has been successful for twenty years is that the editors have kept "friction" low.  Adding a few classes and <span>s shouldn't be much effort.

Note that some authors write their documents in another markup language, then convert them to HTML.  This proposal would require that they update their software to produce the new classes, or edit the generated HTML afterwards.  That shouldn't stop us from trying this proposal, but it's something to keep in mind.