What does Caldwell firing mean for Manning?

Nothing.  It may reinforce what we know: he’s not ready yet.  Other than that, it means nothing.

PFT tries to read something into it but comes up empty as well:

It didn’t make sense to keep Caldwell without knowing Manning’s status. Perhaps the Colts already know what they will do with Manning, but it’s also possible they honestly don’t know if Manning play again.  If the Colts really want to keep Manning, dropping Caldwell shouldn’t be a deal breaker.

In many ways, Manning is the Colts offensive system. If Manning does get healthy and remains on the roster, we’re sure the Colts can find a coach that can build around his talents.