They do stuff like that now.

This is a video a redditor who recovered from locked in syndrome shared about the system he used

https://youtu.be/pKwnOkEnSvY

Not a bad idea. People do sometimes use morse code in adaptive devices. Some computers have had straws that someone paralyzed from the neck could blow or suck on in morse code to type. But it typically isn't used for people with locked in syndrome for a number of reasons

1 any message system would have to be easy to learn for the user and his caregivers and family and friends to learn. An alphabet board can be learned in minutes but morse code could take weeks.

2 Sometimes people with locked in syndrome only have some of the muscles of their eyes fully functional and these can fatigue. Its easier to do one or two inputs for letters at the slower pace than morse code which would require rapid accurately timed blinks. Jean Dominique actually had the incomplete form and had some small eye face and neck movement as well as describing being able to wiggle his limbs in the book.

3 in some people with locked in syndrome the eyelid control is so poor that they cannot open or close their eyes fully. In this case the only movement they have that is reliably easy to see is looking up. It is extremely hard for even able bodied people to use this movement timed with morse code.

There have been improvements a knock code is most often used today. The letters are in a grid and the row is selected by saying the first letter then that row is read off. Also it gives time for the interlocutor to guess the word in between letters potentially speeding up the process.