In the WWDC19 Session 901 "What's new in Core Bluetooth" they mention the new Transport Bridging Key which allows to connect BT profiles like A2DP via the Core Bluetooth API:
"We've done so this year by introducing a new concept called bridging.
Bridging works by taking advantage of low energy proximity to bring up BR/EDR profiles such as A2DP, HFP, AVRCP.
This will work on all devices that support CTKD and to take advantage of it in your application, it's extremely easy.
You'll use a new key in the CBManagerConnect, and it's called the TransportBridgingKey.
You add it in the option dictionary."
There is no documentation on this feature or the new transport bridging key whatsoever.
What's the state of this feature? Is this scheduled for a later iOS 13.x release?