As far as teaching a dog to use AAC ... It seems like it could be done. It would be challenging and your success will probably depend on how much time and energy you are willing to invest in the project. And if your dog is on-board with the learning process.
When my doberman was a puppy, we tried to teach her to ring a bell to be let outside. She never made the connection and eventually we lost interest, but left the bell on the door handle. Our next puppy was a lab ... and she taught herself to ring the bell without any input from us. She just started doing it and we let her out. Super easy. The doberman still doesn't understand how to use the bell.
Just be aware that if you successfully teach your dog to ask for stuff, it might happen more than you expect or appreciate or under unexpected circumstances. Our lab is far and away the most demanding of our dogs, in part because she is very "verbal" and will bark until we read her mind and figure out what she needs. Heaven help me if my lab ever discovers a foolproof way to ask me to play fetch. She would never stop pushing that "Ball" button. Never.
On a related note, I have taught all my dogs to sit to receive treats and if they offer a sit without being asked, they have learned that I will usually reward them with a little taste of the food I am holding. Basically begging, but very polite and I feel that deserves recognition. So if one of my dogs come over to me and sits sponatenously, I understand that means he wants whatever I am holding at that moment.
So imagine my reaction when I am holding one of our chickens in my arms and my big dog walks over and politely sits down, looking up at me with a hopeful expression on his furry face.
Umm no ... nice try, buddy. You do not get a taste.