Magento 2.1 Release Candidate 2 was released yesterday: http://devdocs.magento.com/guides/v2.0/release-notes/ReleaseNotes2.1_RC2CE.html
And according to the release notes:
You cannot update from Magento 2.0.x to Magento 2.1.x with Sample Data.
I'm wondering what's the reason behing that ?
It caught my eyes because I assume sample data are the same as any merchant data and thus, means you can't update from Magento 2.0.x to Magento 2.1.x