Actually, variations on M-expressions have been created many times in the Lisp world. (Look what you can do with macros!) So far, none of them has caught on. The latest attempt for Scheme is SRFI-266, which creates a very nice infix expression sublanguage. If I were working on a team, I would encourage them to use this, but I don't know if it has enough traction to become widespread.

Haskell's syntax comes from ISWIM, which was motivated quite a lot by m-expressions.

Except in mathematica - which isn’t formally a lisp, but practically it’s used like one a lot of the time.