Over on the XDA Developers forum, user "chaleen" has posted a few pictures of what he/she claims to be a Nexus 4 displayed at the Thailand Mobile Expo 2013. This phone shows to be running a completely new build of Android, JWR45B, using a kernel that was built just weeks ago. The About Phone screen also reads Android 4.3 as the OS version.
Only two pictures were taken of the phone by this particular expo visitor. One is of the camera's semi-new interface which shoves the controls to the side rather than display them in the focus area, and the other picture is the About Phone screen shot mentioned above.
Another XDA Developers forum user, "innocent36", also posted two shots. One shows the Jelly Bean Easter Egg that can be triggered from the About section, clearly reading Android 4.3. The other picture is another shot of the About Phone screen, showing a previously unseen baseband string of "m9615a-cefwmazm-2.0.1700.74." This points to GSM networks.
Based on these four screens, it's presumed that Android 4.3 won’t see any drastic changes in the interface – that will likely happen with Android 5.0 "Key Lime Pie". That said, the new release will likely provide a handful of bug fixes and enhancements as seen with the transition from v4.1 to v4.2.
Droid Life points out that the latest build number is just one of a few that are linked to Android 4.3, following JWR46 and JWR39D. Meanwhile, pasted below is a video taken from the Thailand exhibit showing Android 4.3's updated camera in action.