Because fsspec handles the extensions directly, Foozle does not have to opt in to get the csvbase:// support, all that's required is for the csvbase Python client to be installed. So users of Foozle might start depending on these extensions without Foozle ever finding out about it.

But I guess that's the reality of making libraries, even bugs will be relied on, we really don't have any methods for evolving software ecosystems reliably and compatibly.