I read this one really amazing fic that explored "what if Kavanagh hadn't fainted before being tortured in Critical Mass?" . It was very well-thought-out and I loved it, BUT it had a slightly OOC Dr. Kavanagh, making him an angry, angsty sort. I'd love to see someone try this idea with a canon Kavanagh--a weak, petty person without much spine, but whose motives are ultimately good. You could have him taking medication to prevent the fainting or whatever. Just don't make him grow a spine and keep him in character
as much as possible. If you can add some believable Kavanagh/Weir, I will be awestruck and delighted, because I love impossible pairings. Guilt or pity inspiring her to finally treat him differently is just fine. Failing that, any other pairing is fine too.