The update specifically enables notifications to be sent from ANCS (Apple Notification Center Service) over Bluetooth LE to Pebble. ANCS is a new part of iOS 7 which seems catered almost exactly for the kind of application Pebble is designed for – a service which works with iOS applications to deliver simple notifications. One of the limitations with Pebble previously was that lacking iOS integration due to limitations with the platform, this update fills in the gap and enables iOS to deliver notifications from all applications and system apps, from what I can tell. Apple has a list of categories that APNS works with, such as incoming calls, voicemail, emails, news, and so on, this also seems to extend to all the notifications delivered by third party applications as well. In practice the new ANCS based notifications worked well for me on iOS 7 and an iPhone 5s, although there were a few hiccups where Pebble would detach from Bluetooth while running the prerelease version of the firmware, although Pebble has a fix for this.
Last but not least this update enables Bluetooth Smart (formerly Bluetooth LE) on the Pebble’s integrated Bluetooth controller (TI’s CC256x inside a Panasonic PAN1316 module), which initially shipped disabled. Interestingly enough the implementation under iOS has Pebble show up as two devices, one for Classic, another for Smart (LE). It’s important to note that only notifications from ANCS are delivered on the LE connection, the Bluetooth 2.1 (Classic) connection is used for caller ID, music remote control, installing watch apps and faces, and updates.