Update: Apparently Google is doing something different with the Nexus 9's binary release: there isn't one. According to Bill Yi, a regular Google poster, the necessary proprietary drivers are actually included on a separate partition of the Volantis software image. That would explain why the LRX21L release is almost twice as big as the last KitKat images for previous devices.
Proprietary Binaries are also available for Fugu. No proprietary binaries are needed for Volantis. The proprietary vendor binaries are on a separate 'vendor' partition, which is flashed with the factory image update, should not change for AOSP development builds (only boot, recovery, and system partitions need to be updated).
You've probably been waiting with much anticipation for Google to finally push the full factory images for Android 5.0 Lollipop. Your Nexus devices have been yearning for it too, I expect. Well, there's one image up, but it's for the Nexus 9 (Volantis). That probably doesn't help you much, but at least there's movement.
The factory images are a big deal for Nexus devices as they let you undo just about anything you might do to mess up your device. It's also great for getting back to stock in advance of a big OTA update. The driver binaries are not yet posted, but that usually takes a little while longer. You don't need to worry about that if you're just hacking around with mods and ROMs anyway. We'll keep an eye out for more devices to go live.
[Google Developers – Thanks, DrMacinyasha]