For what it's worth, there are many, many smartphone apps that enable this, both using augmented reality and not, and many other research-level prototypes in th

For what it's worth, there are many, many smartphone apps that enable this, both using augmented reality and not, and many other research-level prototypes in the literature. If you've never heard of any of them, perhaps that's because in practice it's not as great an idea as it sounds.