While that would be awesome, lipsync is a looong way away from being like dropbox.

I seriously doubt you can point to any conclusive, scientific language studies on children that really, definitively, show what level of language development a child would develop on it's own, because such a study would be scandalously immoral and unethical.

And yet there are scandalously immoral and unethical situations that have been studied (though perhaps not scientifically, since there's no control over variables, etc.) Of most recent note is the case of Genie (http://en.wikipedia.org/wiki/Genie_(feral_child)) who essentially spent the first 13 years of her life locked in a small bedroom, usually restrained and only rarely hearing words. As is often true of cases like Genie, the course of normal language acquisition has been disrupted, giving researchers and opportunity to see if various theories properly predict what would happen in the abscence of certain events.

And if that isn't disturbing enough, there's a whole website on similar stories (including Genie) at http://www.feralchildren.com/en/index.php.