No mention of Sailfish OS, which has come from Maemo (based on Debian), which became Meego, then after abandoned by Nokia became Mer and Sailfish?
I mean, sure, they haven't exactly been successful, and their major client - the Russian government - were always morally questionable and are currently being sent back to the Stoneage...
But they are still alive and kicking just about. And Sony have put an egg (just the one) in their basket as a hedge against Google going too far (just as Samsung keep Tizen around (also related to Maemo/Meego)).
And there's also QNX still floating around, which like Sailfish also has (or had) decent Android app support. And LG have WebOS still kicking around in TVs.
So, if someone really wanted to and could be bothered to follow through and sustain it, then an alternative OS could come into the mainstream.
Then again, this is about a government wanting to invade privacy and spy on its citizens. India have a bad track record on it. But hey, that wpuld suit Sailfish as they are prepared to work with questionable entities to make custom versions of their OS.