It just seems like their issue is with Rupp, not Knapp. Right or wrong they still think Rupp is too young and not quite able/ready to step into the role Chooch (and then Ellis) played leading the pitcher meetings. We are just not privy to that end of the job, or, possibly, their analytics, but it's obviously about more than just what we can see (on both the field and the stat sheet).
If they were to go out and sign a veteran starting catcher, Knapp would probably be the back-up, and if he did well enough, get as many as 80 starts.
I still think a trade of either Rupp or Knapp is likely, but they could also keep Knapp, sign a fringier veteran catcher (not that Ellis isn't pretty fringe at this point) and see how it shakes out. Given it's a high-injury position, burying Knapp in AAA as the back-up/DH (if he can't beat out the vet) for at least a half-season wouldn't be the worst thing in the world. But all reports are they just aren't willing to go with two young catchers, and that has to be about the pitching staff as much as the catching position itself.