I think in general R7RS-large is supposed to be what mainline implementations implement with R7RS-small mainly being for implementations used for embedding sche

I think in general R7RS-large is supposed to be what mainline implementations implement with R7RS-small mainly being for implementations used for embedding scheme as part of a larger application (and even then you might still use large) as well as for experimental/hobbyist implementations. Particularly if you are just using scheme as a scripting language which mostly calls out to C, it doesn't necessarily make a bunch of sense to include complex features like reflection or weak boxes. Such an implementation might not even have a GC in the first place and just rely on the scheme process ending to release memory back to the OS.