I would love to be able to see inside the mouths of the speakers of other languages. As someone who learns a language online, my access to phonetic knowledge is lower than I would like it to be. It's made worse by my language of choice which doesn't have much information available on the phonetics, to begin with.
When I watch natives show me how they pronounce their basic sounds, I can't see beyond their lips and into their mouths so I still wonder if my tongue position is right on even simple sounds.
I'd love to be able to see native speakers both pronounce their language as well as speak naturally where a camera of some kind is recording footage from inside the mouth.
I wonder how it'd be possible. I imagine some kind of light source would be necessary, though.