I guess Windows Phone 8.1 actually exists after all. Microsoft has just achieved Bluetooth SIG certification for the OS, which is now officially Bluetooth 4.0-capable.
The certification does not include the usual Bluetooth 4.0 proximity protocols, but hopefully this is not an indication that these will not be supported. Also of note is that the protocol will support activating Voice Recognition over Bluetooth, presumably to trigger that brand-new voice assistant we have all been hearing about.
Current rumours suggest we will be seeing Windows Phone 8.1 announced in April 2014, and we will likely see an avalanche of leaks in the run-up to its release.
See the certification at the Bluetooth SIG here.