This is quite interesting and important. Do you have anything I could follow or some literature about the topic? I'm not even sure what to search for as I never thought about alternative modes of communication.
I'll ask my wife who is a BCBA to share any studies related. The premise is symbols to help a kid reach from using symbols to letters/words. Right now they print a ton and velcro them to a board and communicate a complicated topic. There are apps out there but they kind of are lacking IMO and hard for a kid to figure out.