Bash extensions are cool to have in the interpreter. I really don't think we need more than the basic POSIX shell for most scripts. I once wrote a tar replacement in it, with a restricted YAML generator and parser and a state machine — don’t judge me, I think I was manic — and the result was weirdly beautiful.
The lack of arrays, dicts and local variables when trying to be POSIX compliant becomes quickly annoying when writing big programs though. There are of course workarounds to deal with those but I wish we didn't have to use them.
