Many people that have their hands on a Nexus 7 (2013) are seeing a system update notification land on their tablets indicating an update to a newer build of Android 4.3. The update weighs in at just 8MB, and the only noticeable change to our eyes seems to be a build number jump to JSS15R — not to be confused with the previous update to JSS15Q a few weeks ago.
Those who have the update are still working to see what exactly has changed on the user-facing side, if anything. In the meantime most users have yet to see the update and are patiently tapping their fingers on the "check now" button of their Nexus 7. If you have received the update and notice a change, hop into the forums and let everyone know.