You don’t have an area for kudos, but you need one!
The sign language tool is not really working for me yet in Beta (a note about that later) but it’s brilliant none-the-less for making an accessible book that might actually help deaf children learn to read.
However there is another potential application which I would like to put out there.
In transitioning from reading one language to another it is helpful to both hear a sound or word AND see a visual of how the mouth looks while saying it. This could include such comments like “put your hand here on your neck, and feel how your neck vibrates when you say…” (voiced consonant).