My theory about Android 4.3
We can practically be certain at this point, as ryan_socio and the leaks have pointed out, that 4.3 is basically completed. No more time is being spent developing it. So, to ask the obvious question, why haven't we received our update yet?
My answer: Key Lime Pie. Now I know what you're thinking. You're thinking, "Augh! Not another prediction!" Well, this is different. Android's fifth birthday is this October. It would be an incredibly Googley thing to launch version 5 of their software on that birthday. I'm certain it will happen. Judging from past events, I'm also making a pass at the day, but this is less certain: the 29th.
So now we know 5 is coming in October. (most likely) So, once again, why haven't we received the 4.3 update yet? I think the answer is that, with so many new features to be introduced in 5 (speculating here), it wouldn't be healthy to release an incremental update so close to a major platform release. This is also a good opportunity to let OEMs catch up in terms of software upgrades. This is the right thing to do. Incremental updates will only split the platform further, and, as Android Police has proven, the new features in 4.3 work on practically all devices. This will likely mean the camera and gallery will join the Play Store, just as the stock keyboard and calendar apps have.