Though being reserved for return statements, the upArrow ^ could perfectly be accepted as a character composing a binary selector, like the verticalBar | already is.
Indeed there is no ambiguity, since the return ^ is always prefixed, while a binary message never is...
(well, except in the method source, but method source must begin with selector, it cannot begin with a return statement, so no ambinguity there neither...).
I don't plan to use or add such selector in core Squeak/Pharo, but I think that it is important to allow a variety of selectors : it allows the most simple DSL : one using Smalltalk syntax (no need to define a new syntax, a new parser, etc...).
If we did it for |, I don't see why we shouldn't for ^.
Note that we recently also extended usage of - at any place in binary selectors (it was restricted to first position previously), though no core message is concerned so far.
The main objection could be that a missing period before a return statement won't be reported, but interpreted as a message send... like in:
��� x := a+b
��� ^x
But I don't think it's really a feature stopper.
It's very easy to modify the old Compiler and shouldn't be that hard in Opal too.