I would buy that for Mary Russell-verse! Although I've never read much of that verse, I'm not entirely sure that Watson is still his moirail in it though.

I don't think we know enough from any of the canons to guess at Irene's kismesis, but in pretty much all of the tie-ins and fic I've read that addresses the question, he is obviously the King of Bohemia. Except when he's Holmes. But Holmes already has a kismesis of course.

Oh, god, if we keep this up I'm going to fill entire quadrants for every character in bookverse.