GNOME 3.12 will arrive this week and the GNOME Software package has been made ready by Richard Hughes. Some of the improvements include auto-generating a star rating (based upon integration support with the installed desktop/language support, if its updated upstream, etc), support for still using GNOME Software while applications are installing, support to create/modify application folders, and other new features.
With GNOME Software 3.12.0 being cleared, the app center's code-base is already open for new developments. A feature that's already landed for the road to v3.14 is using the AppStream Glib library for faster performance. Other user-visible changes are planned for the next development cycle.
More details -- and screenshots -- on the GNOME software center changes for the 3.12 desktop update can be found via Richard Hughes' blog.