A new Android L Developer Preview is now available, launching alongside the Google Fit SDK release. As the Developer Preview page explains, this is a "special" build with support for the fitness program, so don't expect to see new features or visual tweaks.
The preview build has been bumped to LPV81C, and is available for the Nexus 5 and the second-generation Nexus 7 only. Of course, it's not suggested to use the builds for anything other than development purposes, as it is still incomplete and contains bugs that need to be worked out. Then again, if you're used to installing nightly builds of custom ROMs, you'll be right at home.