Maybe consider chained comparison operators early textual replacement along the lines of the C preprocessor, although the exact textual replacement would involve temporary variables to avoid multiple side effects and be more complicated than just "(a) == (b) and (b) == (c)". (a==b)==c does not expand, only the version without parentheses expands, so you can still do the boolean comparison if you want.
But then is the mathematical '=' really a binary operator that maps two numerical inputs to a boolean output? It feels then as an abuse of notation if (A=B)=C doesn't allow A=B to change type?
Because I don't really have much use for a symbol that is some times doing a binary mapping from numbers to booleans and some times becomes some sort of ternary operator which maps 3 inputs to one boolean.