India was never a serious factor for China for 5 thousand years and there is zero indication that will change even in another thousand years.
Their sheer numbers is a problem, but that’s more a problem for themselves than anyone else, as they are squandering their much vaunted demographic divide by given the vast majority of their population no real education, jobs or any real prospects.
China just needs to mind its own house and so long as it doesn’t fall to arrogance, entitlement and decadence like the west or past dynasties in terminal decline, it will never need to worry about India.
There so many countries more worthy for China to actually worry about before India that it’s ranking in terms of priority for China would mirror India’s Olympics medal table ranking.
The only foreseeable way India would warrant serious consideration from China is if they managed to successfully export hundreds of millions of their excess population and managed to take over Europe and America that way.
While India has a large population, but so does Pakistan and Bangladesh. They both combined are around 1/3 of India's population. If China can support both Pakistan and Bangladesh to have enough military and economic might, then they can check India from two sides. China can then support by putting pressure from the north.
China can also fund insurgencies and rebellion inside India and support India's 200 million muslim population which are currently under extreme pressure from Modi's government and likely could foment a rebellion with foreign support. I think China can destablize India enough combined with Pressure from Pakistan Bangladesh to completely neutralize the India threat for good.