1. This is an interesting development. Hinduism, strictly speaking does not allow re-conversions. Even jumping from one cast/class to another through marriage is a very recent phenomenon. Judaism is another such exclusive club. To be a Jew one needs to be born of a Jewish mother. A Jewish father's off-spring from a non-Jew is not a Jew.
2. Continuous intermarriage has caused concern in the Jewish community because of certain diseases related to this practice. Therefore, at child-birth Jewish women need special medical attention in addition to rituals like yoledet and niddah . Jews are also looking for good seeds to be introduced. That is a service people like Amartya Sen, Dr Mohammad Yunus and Imran Khan have provided.
3. Hindu thinkers/philosophers from the last two centuries have pondered over their situation which can only mean eventual disappearance of Hinduism through natural process. Their demographic curve viz-a-viz others has been travelling downwards constantly. In Bengal's history there is the fascinating tale of Raja Raja Ganesha. In 1414 seizing control over Bengal he faced an imminent threat of invasion. Ganesha appealed to saint Qutb al Alam, to stop the threat. The saint agreed on the condition that Raja Ganesha's son Jadu would convert to Islam and rule in his place. Raja Ganesha agreed and Jadu started ruling Bengal as Jalaluddin Muhammad Shah in 1415 AD. Qutb al Alam died in 1416 AD and Raja Ganesha was emboldened to depose his son and accede to the throne himself as Danujamarddana Deva. Jalaluddin was reconverted to Hinduism by the Golden Cow ritual. This required him to travel under a cow made of gold. (Obviously the gold went to the temple under the Brahmin priests.) After the death of his father he once again converted to Islam and started ruling his second phase.
4. There are now three schools of thought in the subject:
a. The conservatives stick to their guns and preach that there is no place for non-Hindus in SA (historical Bharat).
b. The modern liberated school doesn't want any interference by the clergy in the personal choice made by individuals. They say, let things move as they do.
c. The third group emerging sees the threat to their existence if ancient rules were followed to the letter. They, therefore, propose a system of re-conversion. There again there are differences in opinion regarding the status of the returnees. Some say, make a new low cast of these. Some feel they should go back to the original cast. Etc.
Re-conversion is termed as Shuddhi ( Shuddhi - Wikipedia, the free encyclopedia )
5. Then there are others - and this group has shown some strength in recent times, who look for gradual absorption of Muslims, Christians, Sikhs, Buddhists and others into Hinduism through various means. Indian Constitution considers Sikhs, Buddhists, Jains and Brahmos as Hindus.Only Muslims and Christians are recognized as non-Hindus. For instance, Muslims following a sort of Din e Ilahi are more preferred. Take the case of Bollywood. What is common among the most successful Muslim heroes - Shahrukh Khan and Amir Khan? They both have Hindu wives who practice Hinduism - which is not allowed in Islam.