CM has source? I think Google is waiting on the Nexus 9 to release source. They always withhold source until the Nexus device that launches the new version is released. Then they release source and CM and the others start building. KitKat didn't get a Nexus device; if you remember, it was released on Halloween (31 October) last year. It was just released, source and all. And CM had releases inside a week. There's a developer preview out, but it's beta and has issues even in the official binaries. I'm not putting it on my N7.
We're getting L within 90 days from HTC. Then you'll see the Sense-based ROMs get it. But I imagine CM will beat HTC to the punch, so all the AOSP-alike ROMs will get it long before then. CM, LiquidSmooth, and such.