Most people familiar with the Nexus program know that each new Android update usually brings with it a new set of driver "blobs" for each supported phone and tablet in the product line. Even though these proprietary binaries are usually the latest versions when they come out, Google still occasionally receives updates to the drivers even when it's not a good time to issue an OTA. As we've just witnessed from the long lead time on the 4.4.3 release, it can take quite a while before an update is rolled out. However, it looks like Google is moving to combat this issue by adding a public channel for "Preview" versions of those binaries.
Source: Android Developer's site
In a recent modification to the Android Developer site, a brief description was added for the new Preview packages along with a link to the download page. There aren't many details, but the wording implies that updated binaries will be released in between official firmware updates and with higher frequency.
This may also be intended as a solution to a few previous incidents where changes to the master branch of AOSP resulted in incompatibilities between a driver and the latest source code. The updated code is usually based on these newer drivers, so it should serve to mitigate these inconsistencies.
Whatever inspired the plan to release these Preview drivers, it's certainly a good thing for anybody building custom kernels or compiling the absolute latest AOSP source code to run on a Nexus. Newer drivers more often - what else is there to say?
Thanks, Peter Kiddier.