1) Do continuation marks make it possible to provide delimited continuations? If so, they should be included at least in the examples and maybe in the spec as well, so as to have only one non-portable SRFI rather than two.

2) You should spell out the relationship between the Racket and SRFI 157 APIs.

3) Inferior Scheme is a good thing to have for doing non-portable SRFIs. I think it should be removed from this SRFI and promoted to a separate repository. However, it needs comments to explain how it does what it does (both "interpret Scheme" and "provide continuation marks"). That way other SRFI authors can extend it as needed. By tagging a specific release in the Inferior Scheme repo as associated with this SRFI, people can see it the way it is now when understanding SRFI 157 while allowing continued evolution.