This is an interesting approach. Use #TheStacks for storage, but encrypt your stuff before it gets there
http://qttr.at/1uyw
But it uses a client side proprietary encryption, It would be better to use encfs as an overlay to your cloud storages.
TahoeLAFS does similar without depending exclusively on #TheStacks for storage.
https://tahoe-lafs.org/trac/tahoe-lafs