That question has been open for a long, long time.
Take 5 nations for instance: Punjabis, Sindhis, Nagas, Mangalorean Catholics and Keralites
Keralites and Punjabis have their defined "areas", but they are spread throughout India, so a separation of their nations would make those outside the border to be suspect
Sindhis don't have any area of their own, so what about them?
Nagas have a defined historical area, but their nation is too small and economically not able to cope on its own, plus they work outside the borders for remittances
Finally, Mangalorean Catholics are from South Canara which has 3 (or 4) different linguistic and religious groups in near equal proportion. Breaking this up is impossible or at best very bloody