In SRFI 139, you mention that Guile and Racket also implement syntax parameters. 

Guile seems to make no difference between keywords defined by define-syntax and keywords defined by define-syntax-parameter thus complies to the proposed fix.

Racket does make a difference and does not allow to syntax-parameterize quasiquote, for example.

Rapid Scheme is my own implementation and is easily adapted to the fixed SRFI.

For Schemes like Racket, the code like the following duplicated for all keywords in question can be used to make them comply to the proposed fix of the SRFI:

(import (rename (scheme base) quasiquote scheme-quasiquote))

(define-syntax-parameter quasiquote

  (syntax-rules ()

    ((quasiquote . args) (scheme-quasiquote . args))))

So it is not a big deal.

Marc