Last Updated: June 2nd, 2014
Back on Halloween, Google promised that proprietary binaries and factory images for the Nexus 4, Nexus 7, and Nexus 10 would arrive shortly after devices received their OTA updates. Even though some OTAs haven't even rolled out yet, as of a few minutes ago, all modern Nexus devices now have Android 4.4 KRT16O factory images and drivers available for download.
This means you can flash stock Android 4.4 onto any supported device, even if an OTA either wasn't available yet or wouldn't work for some reason.
Last Updated: November 17th, 2013
Following closely behind the 2012 and 2013 Nexus 7 KitKat OTA updates, it's finally the Nexus 10's turn to receive the same treatment. You can now flash the 219MB KRT16O Android 4.4 build without having to wait for your tablet to alert you, no matter what your rooting/bootloader situation is. Of course, if you've modified the system partition in such a way that the OTA won't apply cleanly anymore, you have to either revert those changes or wait for the factory image.