Hey @nefarius firstly I would like to thank you for all your hard work all over those years, as I can't ever recall for how long I've been using tools/drivers you've developed, mostly SCP Toolkit and ViGEm Bus Driver.
I just discovered this thread (and read it entirely) and knowing that a solution that allows communicating wirelessly with DualShock 3 controllers on Windows without needing to "sacrifice" an entire BT Adapter is already a possibility indeed is awesome! Your earlier posts, however, made me raise a question not entirely related to BthPS3, but I need to ask anyway.
I don't know if that behavior is exclusive to newer DualShock 4 controllers (CUH-ZCT2U) but if you connect them through USB Cable (or Bluetooth through Sony's Wireless USB Adapter), Windows will see the regular HID Input device and also an Audio device, which allow using whatever is attached to the DualShock 4 headphone jack out of the box, without any 3rd party drivers or apps, including the mic in case of a headset.
However, if you connect the DualShock 4 through Bluetooth, then only the HID Input device appears. Earlier on this thread, you said DualShock 4 controllers also try to communicate through PSMs 0x11 and 0x13 before being denied and settling on PSM 0x01. It's clearly out of the scope of BthPS3 driver but do you think that perhaps it would be possible to send/receive audio to/from the headphone jack and maybe to the internal controller speaker by communicating with the DualShock 4 through those reserved PSMs instead of the default "PC Mode" the controller falls back?
Audio obviously can work wirelessly as the PS4 itself does that and it also works on Windows if you're using Sony's Wireless USB Adapter, but I find curious how PS4 is nearing its end of life and DualShock 4 audio transmission through Bluetooth seems to remain unknown territory even after all those years...