In all my years of living in India, I've not come across one person using anything other than English. Most people, even in IT, hadn't the slightest clue about how to type their own language into a PC. Didn't stop them from being "proud" of <insert object> though.
In fact had Google launched the app only in English or English+Hindi I would have been really surprised because they would been losing on the clear majority of India - the rural India, 2nd tier cities, and town and below. Internet is exploding there, clearly engendered by Reliance Jio and other operators following close and in panic.
Also, the way Govt went all guerrilla on demonetisation (nationwide) and the way Govt is pushing digital money the larger population, who are not at all proficient in English, will have to come on board the digital payment system (and in my humble opinion will have to suffer a lot because planning and infra neither are well prepared; but that's another matter) and for the inclusion of regional languages are not a smart move per se, but a must.
GBoard also makes it much easier to write Indic languages (transliteration from Latin etc)