I just came across this thread and wanted to chime in.
I'm the main developer of the (yes, yes, unofficial) ownCloud client for SailfishOS.
The client has been on the Jolla store for some time now but
2 months ago we got a nice little backup daemon running, which will be pushed to OpenRepos as soon as v0.3 is approved.
I should have advertised this earlier, but oh well.
So, if anybody is interested and can't wait until v0.3 hits the Jolla store (v0.3 is a pre-requisite for the daemon), you can grab the source from: https://github.com/beidl/harbour-owncloud
Note that building and running installs both the app and the daemon on the phone.