A united India would mean I or my parents are never born, and my family remain as Hindus in a Muslim-majority land. Leaving aside this personal, rather selfish goal, I think the lack of military tension and saber-rattling enables better development because this united India would only feel a threat from China, which is separated by the huge Himalayas and rainforests of Southeast Asia. And India never officially allied with either the US bloc or Soviet bloc during the Cold War, so this India follows the nonviolent ideals of Gandhi better than OTL. There are worse insurgencies, especially with the Balochis and Pashtuns who are very hard to assimilate under an "Indian" identity.
I can see India letting them loose in the 1960s as protectorates or separate nations, with the Pashtuns probably getting absorbed by Afghanistan. This annexation would strengthen the Pashtuns in that country, perhaps keeping the monarchy in power there and staving off the Communist coup and Soviet invasion there.
The Balochis would probably try to secure independence of the Iranian Balochistan, leading to a civil war in Iran and repression by the Shah of Balochi insurgents. The war could easily see an earlier ousting of the Shah, along with the potential for Azeris to try and secede from Iran and join the Azeri SSR, with generous Soviet backing.
India would see a great deal of communal tension and rioting, which would subside after 10 years under the strong leadership of Nehru/Gandhi/Ambedkar/Jinnah/other guys. The Congress Party would be secular in order to keep the country united, but would lose dominance earlier bc of strong Islamic parties looking to enhance regional autonomy and Hindu parties seeking to counter that influence. The Sikhs would also be as restive. This India would become decentralized and chaotic, but somehow held together like OTL India.