I notice that a number of questions are "unanswered" because in a comment it is pointed out that said question is answered on MO. Could there be a tag "answered in MO" (or "Answered elsewhere" as suggested in the comments) that could be created so that one could add it to the question?
This is an old issue (see also this post and this discussion suggested in the comments) of course, but this seems implementable and useful since one could filter it out when browsing unanswered questions.
[a development which I remove as it upset the author of the question I mentioned.]
But I see now that apparently a lot of very active people of this site are not bothered by this situation, so I'll get back to cultivate my garden, as Candide said.