If our dream that India should be one whole and not the sum of its parts is to be realised, a common lingua-franca is a pre-requisite. And, no Indian language other than Hindi will fit the bill. Out of the estimated 1,618 Indian languages, many without a script, Hindi is arguably the richest and certainly the most widely spoken language in India.
All said, any attempt to thrust Hindi on people of other mother tongues would only backfire as it would be justifiably construed as an attempt at enforcing Hindi's hegemony. The recent exhortation by the Union home minister that all Indians should sign in Hindi is a case in point. Hindi must be promoted but not at the expense of regional languages that have their own unique identities and heritage. In the guise of making Hindi the rashtra bhasha, any move of 'robbing Peter to pay Paul' would have undesirable consequences.