I’ve been working on a PR in vim trying to upstream some of the great work done by this plugin.
I don’t know Guile really well. Is there something that can make it easier to check if the current .scm file is a guile file or a scheme file? I know that guile is a implementation of scheme but since we’ve decide to make a hole new filetype (witch is kind of a mode in emacs) I need some robust way to do that.
I am not an expert, but it may be the case that (define-module …) is a unique Guile thing.
Seems like no according to this documentation and while Chez Scheme seems to not include it OOB, it seems like it may show up anyway as its implementation is in the manual 
(No idea if these sources are reasonable, haven’t done much in Scheme myself either)
Maybe you could look at the heuristics geiser uses to determine the scheme