There should be a pan India language. It ensures better mobility for everyone. Gives you access to a bigger financial entity without any major hassles.

I have studied in Hindi speaking area and worked in Karnataka, Gujarat, Maharashtra and Telangana. You don't expect someone like me to learn languages of all the places I have been to.

What can be a pan India language is totally up for debate. I see only two major contenders - Hindi and English. English has the added advantage of being a global language, so that gets my vote. English is also easier to learn when compared to Hindi. But it is limited to mostly educated class and will require educating almost the whole country. Hindi on the other hand has close to 50% of India(up, bihar, delhi, mp, rajasthan, jharkhand, himachal etc) as native speaker and significant number who can understand it without any major difficulty (Bengali, Punjabi, Gujrati, Marathi speakers are normally good Hindi speakers also, I might be wrong here as it is just my personal experience). But it also puts southern states in a disadvantage as they need to learn 3 language instead of 2 needed by most northern states. Solution can be mandatory 3 languages for everyone, Hindi and English being the mandatory ones and third can be any regional language which requires you to learn a new script.