Does that suggest that you could arrange a kind of course that all children got, which taught the union of all phonemes of all common languages, without teaching much of the languages themselves? And thereby future-proof the child with the bits you can't learn as an adult, in case they wanted to learn any particular language later?
Probably yes, and I think this is what a lot of rich people do with their kids, at least in terms of exposing them to vastly differing languages like Mandarin and English.
I do wonder if there's some limit on the number of phonemes you can learn, and how many hours are required to "solidify" a phoneme. But I definitely think the idea of a "unity course" is a good one.
Personally I had a French "class" in elementary school, where I barely learned anything - I certainly can't speak French - but I can pronounce French words better than I can pronounce any Spanish words (despite three years of Spanish class in college). Those French classes were basically just learning to count to 100 and singing songs like "alouette."
