As nice as fish is, it's not fully posix compliant, leads to some weird bugs here and there
The "expect it to work, didn't" is more on the user's side, going from e.g. bash to fish.
:set shell=/bin/bashThe only trouble is, such snippets have a way of sneaking into documentation, ci pipelines and other places.
And then non-posix isn't quite as nice anymore. Even if csh or fish might be the nicer language.
I do think the oil shell project is on the right track, by trying to "fix" shell (and fish is a great source of inspiration for the interactive part).
Still, when plan9 didn't manage to take over, I guess I'm a bit sceptical about any new shell having much success...
They have considered a compatibility layer in the past:
https://github.com/fish-shell/fish-shell/wiki/POSIX-compatib...