"Support for file encryption (e.g. non-trusted servers)" is the top voted requested future.
However, the justification is out of date. encfs is available on Linux, Mac, and Windows even my Raspberry Pi. It works fine with Syncthing, BTSync, GoogleDrive, etc. I think adding this feature would be duplicating an existing tool chain.
The only problem I've found is how Syncthing handles fuse mounts. To do "--reverse" encfs, Syncthing needs a command line option like Unison to declare a directory as a mount directory and then ~not~ propagate absence of files when the mount is not in the mount table. Easy fix/add maybe?!
I am accumulating documentation of doing this on a web page. It is DRAFT as of mid-February 2017, so please don't axe me yet, however feedback appreciated. http://increa.com/computers/encfs-clouding/index.html