Thank you for including s7 in srfi-177.  I thought you might like an
hygenic
version of that code:

(define-macro (keyword-lambda formals-and-keys . body)
   ((lambda (formals keyword-symbols)
      `(with-let (unlet) ; or (inlet (unlet)) -- more explicit
	(lambda* (,@formals ,@(map (lambda (sym) `(,sym #f))
                                    keyword-symbols))
           ,@body)))
    (split-last formals-and-keys)))

I think the keyword-call macro is already hygienic.  "with-let"
evaluates its body in the given environment.  s7 has
first-class environments, so it doesn't need define-syntax and
its friends.

Here are tests, similar to yours:

(define (writeln x) (write x) (newline))

(let ((lambda* gcd)
       (list abs)
       (a 321)
       (split-last 42)
       (cond if))
   (define y (keyword-lambda (a b (c d)) (list a b c d)))
   (writeln (y 1 2))
   (writeln (keyword-call y 1 2 ()))
   (writeln (keyword-call y 1 2 (c 3)))
   (writeln (keyword-call y 1 2 (d 4 c 3))))

(set! list abs)

(define z (keyword-lambda (a b (c d)) (list a b c d)))
(writeln (z 1 2))
(writeln (keyword-call z 1 2 ()))
(writeln (keyword-call z 1 2 (c 3)))
(writeln (keyword-call z 1 2 (d 4 c 3))))

Please let me know if I've missed something!