@reiver
Today "ActivityStreams: Where do you want to go to today?" might be a slogan we borrowed from Microsoft.
The question is whether #ActivityStreams should be used - besides all the things it is already being used for - to also map to file systems.
The #LinkedData nature of #ActivityPub is generally shunned in favor of plain #JSON. That in itself is fine, as long as:
a) information still represents valid #JSONLD.
b) information models still follow data modeling best practices.
c) information models are designed with #interoperability in mind.
Not saying your approach is good or bad, just observing that everyone mapping and overloading their own app-specific semantics to the poor AS vocab looks to me a worst-practice. We can get away with it, as we made post-facto interop the poor man's accepted practice, lacking more rigorous extension process and guidance.
There are likely existing standardized ontologies.