> MN-W was able to retrofit it into syntax-rules, but it's not portable to do so.  Here's what that looks like:
>
> (define-syntax foo
>   (syntax-rules ()
>     (foo (foo-operand))
>     ((foo obj ...) (foo-operator obj ...))))

I don’t understand this. Is there a link for M N-W’s implementation of whatever this is? R6RS syntax-rules can do this too, because it's nothing more than a simple wrapper around R6RS syntax-case, although I think the clauses have to the in the opposite order to your example or the latter one will never match.