I didn't know that codec handling was done at the hardware level. Interesting.

So the underlying idea of my post ("you can't just add new codecs in software") is ultimately correct, but for reasons completely unrelated to what I mentioned. That is, I'm wrong, but sort of stumbled into the right answer. Doubly interesting.

Now I have a ton of questions about how bluetooth audio is produced on the phone side, so that headphones only have to decode one (or a few) codec on the other side.