At I/O 2014 Google showed off Android L, the next major update for its mobile platform. It is still going to take a few months before the software is going to be released to the public. However Nexus 5 and Nexus 7 (2013 Wi-Fi) owners have been able to play around with a developer preview that Google only released for these two devices. The vibrant Android developer community made sure that Android L was ported over to the Nexus 4 as well. Initially the port had many issues but the latest update of the Android L port for Nexus 4 brings many improvements.
The first beta of this developer preview port had numerous issues with the camera, NFC and Bluetooth. This update takes care of all of those issues. However SuperSu still isn’t working on Android L ported to the Nexus 4 but Superuser from Koush works to fulfill any rooting needs.
Since it is a developer preview, and an unofficial port, its safe to say that you won’t really be able to use it as a daily driver. Apps will crash since they’re not fully compatible and the system itself will be buggy.
It goes without saying that you do this at your own peril, so if you haven’t messed around with Android at this level before, it would be best to read up on it first.