This would be received very poorly by most of the sub-continent, and apart from being just controversial would be impossible to actually enforce.

Those familiar with the political tensions in the South (especially Tamil Nadu) between Dravidian Languages & Indo-Aryan, would point out that you'd have better luck getting them to switch to English than Hindi at this point.

http://en.wikipedia.org/wiki/Anti-Hindi_agitation_of_1937%E2...

http://en.wikipedia.org/wiki/Anti-Hindi_agitations_of_Tamil_...