The impression I got from this podcast was that the Caste System was quite vigorously enforced and self-sustaining within society; to the extent, for example, that even Ashoka The Great's (Buddhist) legacy was able to be largely eradicated over time by the Hindu majority. (And I suppose that I am assuming, implicitly that the Caste System is not compatible with Christianity or Islam either). I'd love to know what the experts think.

Your question seems self-contradictory. If people live in a system that dictates who they are based on birth, wouldn't that prevent conversion?

Are you asking if people converted as a way to get out of this system because they're from a lower caste or Untouchable?