There are at least several users that would benefit from a head controlled input device for gaming. There are a few options for head-controlled mice, but I’m not aware of anything that is setup to be used as a joystick and that would be compatible with the Xbox Adaptive Controller.
The Bluetooth Headmouse (https://www.makersmakingchange.com/project/bluetooth-headmouse/) and the LipSync Gaming (https://www.makersmakingchange.com/project/lipsyncgaming/) would likely be a good starting point, with a suitable enclosure and option to mount to a user’s head, hat etc. The goal would be to take data from an inertial measurement unit, process it appropriately, and translate it into Xbox Adaptive Controller compatible joystick commands.
Is there an existing project out there that would work?
If this is something you’d like to take on, reply here and I’ll connect you with the disability professionals looking for the solution.