I actually think that depending on the evolution of Tengriism you might see a reduction in the caste system of any potential "Gangestan." If they develop a stronger religion, you'll get some sort of religious caste but the rest of Tengriism seems to be a caste demolisher. I know the Buddhists eventually caved into the caste system. So it's possible that if strongly-Tengri turks become Hinduized, the nature spirits/ancestors spirits become the Indian gods... and caste mobility becomes easier since anyone can do acts of piety. I'd say the priestly caste basically scorekeepers and when a person has done enough piety acts they can move up a caste. Thus caste could become a marker for how "pious" and "harmonious" a person is.This is an interesting question. Certainly that the Turks will be Indianized one way or another due to how strong Indian culture was (and still is), I'd say they will certainly embrace Hinduism. But will they maintain aspects of their original Tengriism faith in one way or another ?
Also, will they be able to maintain their Turkish roots and language ? I personally think that both can be the basis of identity of their caste, but how do you think ?
Just some thoughts.