I spent some time thinking about Lorne and Elizabeth (and I don't know if I'll ever get used to him as an "Evan"), and mostly it comes down to Elizabeth not having the ability to affect his career at one stroke. She would have to go through a military intermediary to do that -- and be forced to justify the action, which would put Lorne up for official review. And if she were to abuse that, then it would go straight to the IOA.

I'm not sure it would be an entirely proper relationship, but it's less improper than pairing her with John or Rodney, for example.