[Google Chromecast] AngelDE98:
I've tested some APKs on my OUYA running CM11. I've also tested some before switching to CM11, thus on stock ROM.

Leanback Keyboard: Works flawlessly with the OUYA controller. Doesn't react to mouse input. (Didn't show up when needed on stock ROM)

Leanback Backdrop (Daydream): Looks and works great. (Not tested on stock ROM)

Leanback YouTube: Looks great, but crashes when trying to watch a video. YouTube tries to call View.setZ, which is only available in Android L. (Insta-crashed on stock ROM due to missing blur methods in renderscript)

Leanback Launcher: Unsets the CM theme, resets wallpaper and only shows wallpaper / black screen due to...

W/ContextImpl(26025): Calling a method in the system process without a qualified user: android.app.ContextImpl.sendBroadcast:1187 android.app.ActivityThread.performLaunchActivity:2213 android.app.ActivityThread.handleLaunchActivity:2264 android.app.ActivityThread.access$800:144 android.app.ActivityThread$H.handleMessage:1205
E/AndroidRuntime(26025): FATAL EXCEPTION: main
E/AndroidRuntime(26025): Process: com.android.mclauncher, PID: 26025
E/AndroidRuntime(26025): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.android.mclauncher/com.android.mclauncher.MainActivity}: android.view.InflateException: Binary XML file line #34: Error inflating class com.android.mclauncher.wallpaper.AnimatedLayer
E/AndroidRuntime(26025):	at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2215)
E/AndroidRuntime(26025):	at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2264)
E/AndroidRuntime(26025):	at android.app.ActivityThread.access$800(ActivityThread.java:144)
E/AndroidRuntime(26025):	at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1205)
E/AndroidRuntime(26025):	at android.os.Handler.dispatchMessage(Handler.java:102)
E/AndroidRuntime(26025):	at android.os.Looper.loop(Looper.java:136)
E/AndroidRuntime(26025):	at android.app.ActivityThread.main(ActivityThread.java:5139)
E/AndroidRuntime(26025):	at java.lang.reflect.Method.invokeNative(Native Method)
E/AndroidRuntime(26025):	at java.lang.reflect.Method.invoke(Method.java:515)
E/AndroidRuntime(26025):	at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:796)
E/AndroidRuntime(26025):	at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:612)
E/AndroidRuntime(26025):	at de.robv.android.xposed.XposedBridge.main(XposedBridge.java:132)
E/AndroidRuntime(26025):	at dalvik.system.NativeStart.main(Native Method)
E/AndroidRuntime(26025): Caused by: android.view.InflateException: Binary XML file line #34: Error inflating class com.android.mclauncher.wallpaper.AnimatedLayer
E/AndroidRuntime(26025):	at android.view.LayoutInflater.createView(LayoutInflater.java:620)
E/AndroidRuntime(26025):	at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:696)
E/AndroidRuntime(26025):	at android.view.LayoutInflater.rInflate(LayoutInflater.java:755)
E/AndroidRuntime(26025):	at android.view.LayoutInflater.parseInclude(LayoutInflater.java:839)
E/AndroidRuntime(26025):	at de.robv.android.xposed.XposedBridge.invokeOriginalMethodNative(Native Method)
E/AndroidRuntime(26025):	at de.robv.android.xposed.XposedBridge.handleHookedMethod(XposedBridge.java:631)
E/AndroidRuntime(26025):	at android.view.LayoutInflater.parseInclude(Native Method)
E/AndroidRuntime(26025):	at android.view.LayoutInflater.rInflate(LayoutInflater.java:745)
E/AndroidRuntime(26025):	at android.view.LayoutInflater.inflate(LayoutInflater.java:492)
E/AndroidRuntime(26025):	at de.robv.android.xposed.XposedBridge.invokeOriginalMethodNative(Native Method)
E/AndroidRuntime(26025):	at de.robv.android.xposed.XposedBridge.handleHookedMethod(XposedBridge.java:631)
E/AndroidRuntime(26025):	at android.view.LayoutInflater.inflate(Native Method)
E/AndroidRuntime(26025):	at android.view.LayoutInflater.inflate(LayoutInflater.java:397)
E/AndroidRuntime(26025):	at android.view.LayoutInflater.inflate(LayoutInflater.java:353)
E/AndroidRuntime(26025):	at com.android.internal.policy.impl.PhoneWindow.setContentView(PhoneWindow.java:343)
E/AndroidRuntime(26025):	at android.app.Activity.setContentView(Activity.java:1929)
E/AndroidRuntime(26025):	at com.android.mclauncher.MainActivity.onCreate(MainActivity.java:108)
E/AndroidRuntime(26025):	at android.app.Activity.performCreate(Activity.java:5231)
E/AndroidRuntime(26025):	at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
E/AndroidRuntime(26025):	at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2169)
E/AndroidRuntime(26025):	... 12 more
E/AndroidRuntime(26025): Caused by: java.lang.reflect.InvocationTargetException
E/AndroidRuntime(26025):	at java.lang.reflect.Constructor.constructNative(Native Method)
E/AndroidRuntime(26025):	at java.lang.reflect.Constructor.newInstance(Constructor.java:423)
E/AndroidRuntime(26025):	at android.view.LayoutInflater.createView(LayoutInflater.java:594)
E/AndroidRuntime(26025):	... 31 more
E/AndroidRuntime(26025): Caused by: java.lang.NumberFormatException: Invalid int: "res/drawable-hdpi/panel_bg_holo_dark.9.png"
E/AndroidRuntime(26025):	at java.lang.Integer.invalidInt(Integer.java:137)
E/AndroidRuntime(26025):	at java.lang.Integer.parse(Integer.java:374)
E/AndroidRuntime(26025):	at java.lang.Integer.parseInt(Integer.java:365)
E/AndroidRuntime(26025):	at com.android.internal.util.XmlUtils.convertValueToInt(XmlUtils.java:122)
E/AndroidRuntime(26025):	at android.content.res.TypedArray.getInt(TypedArray.java:255)
E/AndroidRuntime(26025):	at android.content.res.XResources$XTypedArray.getInt(XResources.java:1002)
E/AndroidRuntime(26025):	at android.view.animation.Animation.<init>(Animation.java:246)
E/AndroidRuntime(26025):	at android.view.animation.AnimationSet.<init>(AnimationSet.java:81)
E/AndroidRuntime(26025):	at android.view.animation.AnimationUtils.createAnimationFromXml(AnimationUtils.java:113)
E/AndroidRuntime(26025):	at android.view.animation.AnimationUtils.createAnimationFromXml(AnimationUtils.java:91)
E/AndroidRuntime(26025):	at android.view.animation.AnimationUtils.loadAnimation(AnimationUtils.java:72)
E/AndroidRuntime(26025):	at com.android.mclauncher.wallpaper.AnimatedLayer.<init>(AnimatedLayer.java:61)
E/AndroidRuntime(26025):	at com.android.mclauncher.wallpaper.AnimatedLayer.<init>(AnimatedLayer.java:51)
E/AndroidRuntime(26025):	... 34 more
W/ActivityManager( 443): Force finishing activity com.android.mclauncher/.MainActivity
I/Process (26025): Sending signal. PID: 26025 SIG: 9
I/ActivityManager( 443): Process com.android.mclauncher (pid 26025) has died.

... and yup, that's it. (Not tested on stock ROM)

I'll update as soon as I get a device running Android L.