I think it would be great if ownCloud users would be informed about new major features or changes after an update was applied. This way users can be assisted in discovering new features and don't have to discover them 'by accident' or by reading the changelog.
Nice idea. One more thing to add: In my opinion we should provide a changelog there which can be understood by non-technical users as well, so maybe just TOP5 highlights or something similar.
As a workaround: You can use the announcement-app to inform users yourself. A general notification can lead to confusion when you haven't enabled some of the new features.