Several hours ago, an Android 4.3 system dump was leaked for the Nexus 4. As it turns out, even though the bootloader and the radios weren't included, the system dump is totally bootable. I'm running it right now. If you want to try it out, it's easy to do so, but be prepared to have your bootloader unlocked and flash some zips via a custom recovery. If you don't know what any of this means, I suggest you get familiarized with Android flashing first.
For the past few hours, I've been observing a curious case of Jeff Williams on Google+. Jeff posted a screenshot of what he claimed was a Nexus 4 he bought from a Googler... with a build of Android 4.3 on it. The same build, JWR66N, that we saw leaked earlier on a Galaxy S4 GPE by SamMobile.
In disbelief, some have called him a hoaxer, but a number of resourceful folks decided to get Jeff on IRC (channel #Android43 on freenode) and worked with him for hours, trying over and over to get the magical system dump that would prove Jeff's story to be real.