That might be true, but where ever you go, there is always bash installed. zsh not so much. Knowing the tools, that you will always find, is a pretty useful skill.
That is not true at all... if you install FreeBSD out of the box there is no bash installed. Most of my FreeBSD servers don't have bash installed at all because I don't find it necessary at all, tcsh does everything I want it to do.
If you're going to use a system enough to copy your readline & bash config, it would be just as easy to copy your zsh config and install it in the rare case it's not available.
Hmm, does it? I installed it right away and it's pretty much exactly like fish (history traversal with arrows, case-insensitive matching, etc). I might be mistaken and it might just be omz.