Windows supports a Cloud Files API that lets you "lazily" sync files from a "cloud" into a directory. (Sample)

It would be interesting to see if we can take advantage of this to create "virtual" node_modules/ trees that get lazily synced from the cache into concrete files, as they get accessed by various tools.

This would give the impression of having a fully-real node_modules and work at the OS level, so all existing tooling would "just work", but let us completely skip installing a vast swath of potentially unused files in people's dependency trees.

This would, of course, still require downloading entire packages, but it would be a lot less stuff.