One big flaw about future demographic prediction most people make is assuming TFRs remain constant and not accounting for immigration.

Kerala, for instance, is seeing heavy emigration of Christians abroad while Hindus from UP and Odisha are flocking in.

By 2050, Christians in Kerala may likely drop to 4% accounting for high rates of emigration. Also, their populations will start shrinking after 2023.

Hindu share will rise owing to higher emigration from other states (largely Biharis and Odias).

By 2050, share of Malayalis in Kerala will drop to 77% and the remaining 23% will be mostly Hindus from other states.

In 2017, for every 5 immigrant into Kerala, 2 were Muslims (and 75% of these Muslims came from Bengal and Lower Assam). These Bengali Muslims account for 2-3% of the state population and will flee once NRC starts. They also report their mother tongue as Malayalam on census.

Share of Hindus in Kerala will soon start rebounding owing to higher TFR of Bihari and Odia Hindus.

Bihari Hindus have much higher TFR than even Malayali Muslims btw.

Muslim share in Kerala won't cross more than 32% as their population will peak by 2038.

If TFR of Muslims in Kerala doesn't fall as fast as expected, share of Hindus will be 62% by 2050.

But if their TFR falls considerably, Hindus will rise to 70% in that case.