After CyanogenMod published its blog post about its plans for Android L support, Xposed Framework creator rovo89 is making a similar appeal to the Android community for a bit of objective analysis and a lot of patience. The summary of the situation is that Android L is still a fast-moving target that it isn't practical to work on polishing Xposed for it. The developer would rather release a version that works well a bit later, rather than one that is too early but barely functions.
The biggest factor in this uncertainty of Xposed's immediate release on Android L, even in a preview form, is ART, the new Android Runtime. While Google advertises ART to bring only goodness to end users, for developers, especially those like Chainfire and rovo that tinker with Android's underlying subsystems, it is the proverbial pain in one's extremities. Add to that "enhanced" security features and dual architecture (32 and 64-bit) support, and you have the recipe for a system developer's nightmare.
ART in particular is also still changing a lot everyday. Ever since ART was introduced and even now with Android L already announced, the runtime is still seeing massive code changes and substantial modifications. If it isn't hard enough to hit a moving target when you're making a high-level Android app, it is even moreso when you're developing one that modifies system features from under Android's nose. Like Chainfire and CyanogenMod, rovo wants to focus his efforts only when ART has reached a more or less unmoving state. That's not to say that he isn't doing anything, of course. He does have some prototypes working, depending on how you define "working", but nothing that is fit for any public release. Given the nature of Xposed, users will certainly appreciate a release that won't brick their device instead of one that is hot off the Android L press.
rovo makes another note about the state of Xposed for Android 4.4 KitKat users who have switched to ART instead of Dalvik. Unfortunately for them, they will have to wait even longer. Apparently, ART in KitKat and ART in Android L are quite different beasts, so even if Xposed started working on the latter, it wouldn't necessarily work on the former. For rovo, it makes more sense to work first on getting Xposed to work well on an Android release that only has ART before trying to work on one that can still switch to Dalvik as a fallback.