If there are other people in my position (and I hear people talking about extricating themselves from Google's grip lately) - an alternative pitch might be "Google Drive alternative" instead of "Dropbox alternative"...
Very interested in this. Will wait for Linux support and how well it's implemented.
Currently using Cryptomator in conjunction with cloud services. Even with encryption at rest, I'd much rather do (as /u/nicolasbistolfi called it - did he just coin a new phrase?) fog syncing.