When a person is looking for a way to communicate in alternative ways, they need to find something that really works for them. They need to try to find a voice that sounds natural. They want to try to find a way to be efficient. They want to be able to communicate as normally as possible, even though they're not using their biological voice.
Growing up with Cerebral Palsy I often wondered if I would ever experience my happily ever after. The fairytales my mom read me always followed the life of a beautiful princess falling in love with a handsome prince. You never read about a prince and princess in wheelchairs or with any type of disability for that matter.
Every educator needs to make a decision about technology they need to put in place. They're not sure if they should put Option A in place or Option B in place. This can be particularly difficult in the world of disabilities because there might not always be a perfect answer. Teachers can look to this solution, using the least dangerous assumption to make good decisions about what technology might be best.
When you don't have enough evidence about a student's performance, assume they can do whatever you're asking them to do.