With Windows 8.1 breathing new life into the tablets and making Modern UI on the desktop, somewhat productive and pleasant to use, and true BT 4.0 support coming to the phones, there's only one thing missing now, IMO, from the ecosystem.
Dynamic Playlist sync for Windows Phone. Yes, if you only rip standard CDs you can match them to the cloud and stream, but 1) the cloud don't match much for a lot of people and 2) your listening habits are dictated by #2 when on-the-go. Finally 3) virtually no remixes are in the cloud. Not club or underground.
There's just no better way to manage playlists/songs with a large library than on a desktop. Those changes and the songs in the dynamic playlists should sync and download to the phone as they always have.
This leaves a gaping whole and until it's filled I'll never be able to leave iOS. The sad part is this functionality is in Zune and iTunes, even over WiFi. Sure, you can get it in Windows 8 using media player classic, but MS can't have it both ways. You can push people forward and away from W32 computing and the old Explorer UI, while leaving major functionality out of the Modern UI.
Fill this gap, and I'm all-in.