First, archive -- record the language, its linguistic structure & features for science's and posterity's sake.
Then, coalesce all these regional (particularly North Indian) dialects and languages into Standard Hindi. Standard Hindi itself could perhaps be allowed to evolve by absorbing features from the languages it extirpates and form a "New Hindi".
This would be easier done in the North. With the South Indian languages there's practically not much of an option besides teaching them Hindi, and encouraging Hindi adoption in the home. The South Indian (Dravidian) languages are so different from the North Indian (Indo-Aryan) languages, that they share barely anything in common with Hindi (besides some common vocabulary). Alternatively, the South could be encouraged to switch to English, but this would probably prove too politically controversial.
Finally but not the least, Hindi needs to be turned into a language of the arts and sciences -- particularly in the the sciences, or rather, in all STEM fields (Science, Technology, Engineering, Medicine). Most countries (China, Germany, Korea, France, Japan, the Arab countries, etc.) -- all use their own languages for the majority of things they do. In India, English continues to dominate, perhaps in a desirable fashion -- but at least for the sake of 95% Indians who don't really speak English, it would be good to give them access to the STEM fields without forcing them to learn a totally different/new language.