Big hint towards 4.3
Looking at any of the device photos on the Google Play store, the images of any device correspond to the version number. When the Nexus 7 first came out, it's time was 4:10.
And when Nexus 10/Nexus 4 came out, all pictures were updated to show the time of 4:20.
That, along with news from androidpolice.com about the 4.3 GS4 rom already leaked, I'm pretty sure 4.3 is literally right around the corner. My best bet is with the release of the new Nexus 7 in July.