I think that an interesting topic to research is who identifies whom as a Hindu and for what reasons. I know that there has been some pressure in India to consider Sikhs and other religions as Hindu, and that there is some resistance to considering converts to Hinduism as being Hindu. I am not that interested in the actual criteria as to what makes a Hindu. I have nowhere near the knowledge required to catalog a list of criteria, and I think that it would ultimately be useless anyways. Rather, I am interested in why there is exclusion and inclusion for different groups. I am reasonably sure that I will find various political reasons for considering a Sikh or a Jain as Hindu, as I believe that there are some benefits to being considered the majority religion in an area. I am not entirely sure why some Hindus are resistant to the idea of converts to Hinduism being true Hindus, especially in countries outside of India. It could just be the anti-conversion attitude applied outside of India, but I really do not know for certain.
I do know that the rising Christian and Muslim populations in India is considered problematic by some members of the Hindu majority, as some of their numbers (particularly Christian) are converts from Hinduism. Perhaps some Hindus do not want conversions to Hinduism to count in the same way that they do not want conversions to Christianity or Islam to count. I would not be surprised to find that there are more converts to Christianity and Islam than there are to Hinduism in India, and this could be why there is an anti-conversion attitude present. It benefits Hindus more to be anti-conversion than pro-conversion because they simply have less converts. My research would largely feature India, but I would also like to research “Western” countries as well.