Almost nobody cares about these features for new shells. POSIX compatibility in my opinion is an anti-feature for interactive shells; for scripts, use the shell referenced in the shebang. There are even newer POSIX compatible shells like oil if you want one of these.
It’s not getting POSIX compliance done, that’s for sure. Or compatibility with normal scripts.
Almost nobody cares about these features for new shells. POSIX compatibility in my opinion is an anti-feature for interactive shells; for scripts, use the shell referenced in the shebang. There are even newer POSIX compatible shells like oil if you want one of these.