I think the HTML output should preserve the same semantics as the TeX space commands. That is, "\ " should be breakable (<wbr>&nbsp;<wbr>), and "\," unbreakable (&nbsp;). Full space for the latter because the Unicode real thinspace character is probably not supported widely enough yet. Whether &nbsp; or &#x00A0; is used doesn't seem important to me, results are the same.

Submitting this so we (maybe) won't forget about it, whatever we decide about the final outcome.