I think Hindi/Urdu is quite a bit like Serbian/Croatian. The preferred script followed the religious divide, but (if I understand right) both sort-of standardis

I think Hindi/Urdu is quite a bit like Serbian/Croatian. The preferred script followed the religious divide, but (if I understand right) both sort-of standardised quite similar dialects out of a range of possibilities. And then later they were politically divided, and there were some efforts to move the official vocabulary away from each other's. IIRC Sanskrit has also been written in dozens of scripts, there's a perfect one-to-one transliteration into most (maybe all) the north-indian scripts, although they have extra characters for their own sounds.