As a side note: Phone Link on Windows does allow replying to texts/iMessages on a connected iPhone. However, group messages are not handled properly, and message history from before the connection started isn't available. I believe it's available on an API that is only available on an older version of Bluetooth that is not low-energy. It can also sync contacts and do phone calls.

Over BLE, it is possible to receive and delete notifications, as well as view and control media playback/volume/metadata.