The Gambit R6RS/R7RS maintainer has told me that because Gambit will use a preprocessor to handle both R6RS and R7RS libraries, there will be no support for cond-expand, include, or include-ci embedded in Scheme code: they will only be supported as library declarations and as top-level expressions in programs (and presumably at the REPL). This will be an explicitly documented derogation from R7RS-small.
This effort has now been abandoned.