Mughals never had the capacity military or logistical to maintain this huge Empire just look at the Central Asian Fiasco of shah jehanA Longer Lasting Mauryan empire seems to be the best candidate, though since you didn't mention it has to be Hindu Empire, A Longer Lasting Mughals Might pull this as well
A more aggressive and lucky British Raj ?, which is able to completely defeat the Afghans and take over large parts Afghanistan and is able to annex TibetMughals never had the capacity military or logistical to maintain this huge Empire just look at the Central Asian Fiasco of shah jehan
Undivided British India transition to republuc of India is a start
And then instability in Afghanistan causes India to occupy most Parts and while China the Civil War last for 25 years and in the meantime the Indians occupy the Tibetan plateau
I dont think that is possible prior 1900s, Tibet, and Afganistan have their own nationalist movements. Afganistan already has it's own kingdom, before having British control. And can you explain why would the British Annex Tibet even though it's just gonna be a strain to economy. And even if they have defacto control of it, the world recognized that as Chinese teritory. I dont think Britain would allow themsleves to get pressured by the countries that has interest with China if they placed some bases and other stuff in Internationally recognized Chinese teritory. And I think you cant really stop the british from partitioning india, or if you did the ethnic conflicts that the british rule neutralized might happen again because they might not allow another tribal group or ethiniticy from india to rule over them instead they want to rule India. Or In other words, that is prone to tribalismThe most likely way to create a Super India would be for an expanded and unpartitioned British Raj to gain independence. The British Raj already consisted of what is now present-day India, Pakistan and Bangladesh, while the British Empire controlled Sri Lanka as a separate colony. So Sri Lanka could be added to the British Raj. Also, Maldives and Afghanistan were protectorates of the British Empire. Bhutan and Nepal were also protectorates of the British Empire. Maldives, Afghanistan, Bhutan and Nepal could be transformed from protectorates into full-fledged colonies and then these full-fledged colonies could be added to the British Raj. Furthermore, Tibet was a protected state of the British Empire. Yes, the British Empire acknowledged Qing China's suzerainty over Tibet, but this was just for optics, because the British Empire had a certain degree of de facto control and influence over Tibet early in the 20th century. When you can annex thousands of kilometres of traditional Tibetan territory to the British Raj, you have a certain degree of de facto control and influence over Tibet. So the British Empire could have made all of Tibet into a full-fledged colony and then annexed all of Tibet into the British Raj. That would mean that the British Raj would consist of what are now the countries of India, Pakistan, Bangladesh, Afghanistan, Bhutan, Nepal, Tibet, Maldives and Sri Lanka. A more unified and militaristic population of the British Raj could ensure that the British Raj is not partitioned when it gains independence.