Eventually, most of Google's hardware will get Android 5, though the speed at which this process occurs for older devices might not be to your satisfaction. If you're rocking a Nexus 4 and can't wait for the official rollout of Android's next major update, you can get it now if you're happy to engage in some tinkering.
Photo by Google
An XDA forum user by the name of "percy_g2" has made a preview build available for download. It weighs in at 352MB and going by reports on XDA, seems to run without any significant problems, though Liliputing's Brad Linder says that some users might have trouble with mobile data and certain sensors.
The usual disclaimers apply and you'd be wise to make backups before you delve into the world of flash alphas onto your hardware.