Local filesystem interface to files which exist "only" on the cloud is basically the way Keybase FS operates. If this is a "killer feature" for you, consider giving it a try. The downsides at the moment are (a) alpha software, and (b) 10 gig limit. It is free though, very convenient, and does a lot of things "right" (by my way of thinking).
The major thing it does wrong is that it mounts the directory in the fs root, rather than my homedir. That means it was effectively invisible (if it's not in my homedir, I never see it), so I never used it. Dropbox, on the other hand, is always right in my face at ~/Dropbox.
It's too bad, because kbfs really gets many things right.
https://keybase.io/docs/kbfs