I’m sure not looking forward to head droop. Sounds awful. The brace looks like the kind of device used to stabilize some patients after neck surgery. It looks complex and monstrous, but the concept is exciting.
This article offers some concepts for customizing the headrest for potential switch control (here the focus is drive controls, but of course any switch access applies to eye gaze more generally).
In terms of off the shelf products, Sharon, has he tried the Savant?
If he can tolerate some mild traction (hands on) when he lies down, even just holding his chin up for a minute, that might potentially help.