You definitely need a pre-1900 POD for this. Since the time of Ram Mohan Roy, Indian nationalism was vehemently secular and hotly opposed to Hinduism in government. Even Tilak worked with the Theosophist Annie Besant despite being a firm believer in “Hindu rights” including child marriage (using arguments that sound a lot like Christian fundamentalists’ support of homophobic bakers), and supported placing the Islamic crescent on some sort of Indian flag in addition to Hindu symbols. BTW, it's ASB for Tilak to lead the Indian nationalist movement because he believed that Marathas should be demoted to Shudra status, and Marathas were some of the most important supporters of Indian nationalism. The fact that Hindu nationalists believed that Marathas should be demoted alone discredited Hindu nationalism for decades. Hindu nationalism IOTL only got over that by viewing caste with disdain, to the extent that the current BJP President of India is a Dalit. I think it's very difficult to get Hindu nationalism to get over the caste issue.
All I can really think of is a successful Indian Mutiny, resulting in an independent neo-Maratha Empire led by Nana Sahib with the Rani of Jhansi as his deputy of sorts. I can easily see this state, led by Brahmins (despite its name, Brahmins rather than Marathas led the Maratha Empire as well as the Marathi section of the Mutiny) toy with Hindu nationalism. However, this neo-Maratha Empire would only encompass Madhya Pradesh and part of Uttar Pradesh (an odd place for a Maratha state, but that's where the Indian Mutiny was clustered), so it would hardly be a pan-India state.