I agree with many things you say. Take AWS S3 as an example: it reduces the problem by making objects immutable. Internally, they can cache aggressively without scaling fine-grained consistency on the objects as such. As an S3 user I can aggressively cache on the client too.

Now we've reduced the problem to consistency on the metadata structure which aggregates objects for the user. There are "well known" ways to do this for traditional trees. Other well known options include doing an all search based approach (i.e. always talk to a server for metadata, perhaps with local result caching), and so on.