A build of Android 4.3 for Nexus 4 has been leaked and posted at XDA-Developers Forums ealiar today. Since the original link to Dropbox has now been taken down due to overload, Paul from MoDaCo has posted the mirror link on MEGA. You can download it from there. [Mirror Link on MEGA].
The build is currently in TWRP backup format so you’ll need to ensure you have the custom recovery installed, push the files to your TWRP backup directory on /sdcard and then restore.
Android 4.3 is expected to be officially launched at upcoming Google event on July 24th, however it’s not a big update on the platform.