As someone that is currently carrying a Kit Kat handset and a Windows Phone 8.1 handset daily, I have to say that I am not seeing anything ground breaking in the new version of Android. What I see is the first 'break' in Android with their move from Dalvik to ART. Long term, the move should make Android run longer, smoother and have better graphics than ever before. Short term, it will cause major fragmentation.
Now for those that have been with me on Windows Phone since day one, this is not the same Android that we used back in the day. I have had only 3 force closes in the month plus I've been running it. Skinning the device to look how I want and perform exactly how I want is amazing. Also, the App Gap, yes, I said it, is still huge. Unfortunately, these aren't big name Apps, but things like my bank has a Droid app, but not a WP app. Android has really grown up...
That said, I still give the nod to WP in most areas. Notifications - specifically the 'toast' ones are awesome. The viewable screen with tiles is easier to manage and the cameras are still light years ahead of everything else. I don't think Android L would make me switch, but if WP keeps edging closer to Android, that might.