[botdan]

They publish the CAD files (both mechanical and electrical) on GitHub with instructions on how to manufacture your own expansion cards. I believe the interface within the expansion cards is just standard USB-C. If someone could manage to squeeze all the necessary components within the physical dimensions, it should be possible to make your own soundcard expansion card.

https://github.com/FrameworkComputer/ExpansionCards

[deltron3030]

Maybe addional hardware wouldn't even be needed. Onboard soundcards should be good enough for ASIO (they work fine on Hackintoshs and Core Audio on MacOS). The reason why it's not offered is the licensing I think, it's properietary technology from Steinberg, a German company who invested into Windows pro audio early on and kinda got a first mover advantage there.

I don't know how much licensing would cost, but Framework could possibly offer a driver for the internal card as an addon. Then the slot could be used for a small headphone amp which would be more third party friendly I think.