It seems like your points 3 and 4 could be solved by using a Forth-like syntax. "abc" r<TAB> would only suggest functions that can operate with a string at the top of the stack. Threading code would be `1 1 + 2 /`. There are no parens to match in `h g f`.

Of course it's even more obscure than functional programming (point 2) and if the semantics aren't changed, point 1 isn't solved either.