The official Windows Phone 8.1update will bring Bluetooth Low Energy support to current Windows Phone 8 handsets. It seems Microsoft is laying the groundwork for this by certifying the update with the Bluetooth SIG.
Bluetooth Low Energy or Bluetooth Smart support will enable Windows Phone 8 handsets to interact with Bluetooth LE accessories like the fitbit or Nokia’s Treasure Tag. Support is already present in Nokia handsets on WP8 GDR3, but this was a custom Nokia feature on top of WP8, rather than native support.
Unfortunately there is nothing else particularly new there, including no support for features such as Bluetooth HID, which would enable Bluetooth keyboards, useful for a phablet like the Nokia Lumia 1520.
Hopefully we will see a rash of these certifications over the next few weeks as Microsoft prepares to roll out the update to all WP8 handsets.