Different religions, but not completely different cultural traditions. Panchayat is still the law in a lot of rural Pakistan, the caste system still has strong roots regardless of faith (upper caste Sikhs discriminate against lower caste Sikhs) and, as previously stated, the idea of being Indian is no new idea. Religious nationalism wasn't really a thing in India, and arguably isn't to this day, as Pakistan has struggled to develop an identity of its own beyond 'Muslim India'. Partition contains a lot of complexity and is not as simple as Hindus vs. Muslims.
That being said, there is a gulf between the Dravidian and the Aryan halves of the subcontinent, and if an ATL Revolution happened, while many of the North Indian languages could be folded into Hindustani, Tamil, Telegu, Malayalam etc were actually becoming more diverse. Personally I'm a believer of larger states will consolidate with one another, but historically, whenever an Indo-Gangetic state had consolidated its powerbase, it always moved South, whether the Guptas, Mauryas, Mughals, or Tughluqs. For that reason an Indian unification isn't as far out as people seem to believe.
Another reason it's similar to medieval France is the whole issue of vassalhood. People tend to discount the Nizam of Hyderabad or the Nawabs of Bengal or Arcot from being in the Mughal Empire, but legally and formally they were. The same way Kublai Khan was the Great Khan and his vassals had a lot of freedom, such was the way the later Mughals functioned. And indeed even when they surrendered territory, it was done as a lease; the Durranis ruled Punjab and Kabul in service of the Mughals, although in practice it was all theirs.
Plus up til 1857, the EIC ruled India as Mughal functionaries; there is a direct continuity between Mughal, Corporate, and then Crown rule.