Even if India and China have the infrastructure to support the hosting of the world cup or they have the funds for it as long as they never bid themselves forward as organizers, is it possible for FIFA to appoint one? It seems that it is impossible because FIFA only appoints countries that volunteered because it means they have the ability or desire to become the organizer, because it seems that at this time FIFA is no longer considering the development of football from the countries that bidding to be the host, so every country currently has the opportunity to become a host as long as it has the funds and FIFA sees an opportunity to get bigger profits there.
Well, profitability is a big concern if the matches are being scheduled in India. Because the government never makes these events tax-free and it won't be acceptable for the FIFA. And football is not the most popular sport in India, unlike the case with most of the other countries. And given the current political climate, I don't think that the Indian government will take a favorable view of hosting the event in their territory. In case of China, the scenario is more viable. The government is more supportive compared to the one in India.
I think India or similar countries can't be good options because the world cup should be in a country where there is more interest in football and the government helps to be a better host and have a better experience. Otherwise, there are many other countries in the world to host the world cup.