And that bash 3.2 is one of the reasons I want to turn off rootless so I can install modern bash 4.3 in /bin/bash, so that scripts that have #/bin/bash continue to work unmodified.
Apple will most likely never update their bash to GPL 3.0 bash 4 or later.
It's easy to change your default shell, but if you got a shell script that explicitly specifies #!/bin/sh (and they all do) then /bin/sh will be invoked, regardless what your default shell is. So your options are to modify every script file to invoke your default shell (usually #!/usr/local/bin/sh ) or to install your default shell in /bin.
Apple will most likely never update their bash to GPL 3.0 bash 4 or later.