Funnily enough, I read just recently (though I can't remember where) that John McCarthy originally intended to develop a syntax called M-expressions (derived from Algol or Fortran) for LISP that would be compiled to s-expressions, but users seemed content with the s-expressions and he didn't bother.

Ah, Wikipedia mentions something on the topic:

https://en.wikipedia.org/wiki/M-expression

Plus ça change, etc.