Vash/Milly? I'm sure there is SOME story out there by some author. Though I myself haven't found one (and even if there was one...what are the chances of it being great?).
As for the Harem being canon for Tenchi Muyo...well, it was true for the GXP guy. I can see it being true for Tenchi Muyo as well. Though IMO, that would be a copout (I mean, as fun as having multiple wives might be, when you consider that most people can't even handle one, what makes you think you can handle 6?). Poor Tenchi. :blink: