I don't know of anyone having done this before, though of course someone may've quietly done so for a particular site implementation.
It is interesting. You may want to look at the text-html-procs.tcl file included in OpenACS 4.5's acs-tcl package. It has code to look for unclosed links and other errors that's used to protect against broken HTML in forum posts, etc. It might be wise to run user-submitted HTML through the checking proc in text-html-procs.tcl before putting it up on a site ...
