Welcome @fifthager, great to have you here, and excellent first post, you have certainly done your homework. Your project objectives are commendable. Assistive technology is so prohibitively priced, when it’s often not particularly expensive to produce - captive market I suspect.
The Pi 3B+ unfortunately won’t work yet with our Raspbian Jessie Lite-based Picroft image, however there have been some substantive attempts by the community to this end. It’s something we’re working on - covered in this recent blog post.
In terms of the Skill layer to send raw bash commands, I think this Skill from my colleague @forslund would be a good starting point. Unfortunately I’m not aware on anyone else in our developer community working in this space; and I’m likely to be the person to know 
What I am aware of are other technologies in the assistive space; it might also be worth checking out OpenBCI - they do open source brain computer interfaces for neural interfaces, and that might be another option as well.
Please don’t hesitate to let me know how I can assist further.
With kind regards,
Kathy