Is there a Guix package and service for SchemeBBS?
No.
* The first roadblock is that there are three "mirrors" of the code that differ slightly from each other. This is the most glaring problem.
* The second roadblock is that SchemeBBS uses a customized MIT Scheme 9.2, whereas Guix has MIT Scheme 11.2. This could probably be fixed with some patches to SchemeBBS.