Would probably overcomplicate the POP system. Teaching someone a new language is also rather easy. A person can have multiple languages (Corsica French & Italian, Belgium Dutch & French, Alsace German & French). Changing someone's culture is quite hard (ethnicity impossible without dna altering

). I think paradox made the right decision to tie pops to culture and religion, although in the balkans they mixed the 2, using religion to differentiate 2 groups of the same culture. As for India and Africa, they are beyond the timezone and in order to draw new borders, you'd need to have bloody wars. Africa isn't shy of bloody wars, but they are mostly about who can dictate a geographical area (I'm not even gonna call it countries).
That can already be simulated using the ideological rebels, although it sometimes may seem more like pretender rebels.