I would like to try out India OS when it is finish. Hopefully, it would have a lot of cool apps, and games being made for it when India's mobile OS is released.
I feel India's public schools, libraries, and other government agencies and workers will be the first to use India mobile OS made by India's government because the Indian government would save money if the OS can run well on slower and more affordable smartphones and tablets which are cheaper to buy than an iPhone and modern Android devices. The Indian government can keep supporting older mobile devices with India OS until most of the old devices are broken or too slow to run modern apps instead of buying new smartphones because Apple or Google is no longer releasing updates for older devices and apps.
A lightweight Indian made mobile OS, which runs well on more affordable smartphones/tablets, could be good for poorer mobile users who can't afford an iPhone, Android phones, or higher quality flip phone which can still cost $70 or more at a retail stores like Bestbuy.
I think it may take a long time for another mobile OS to overtake Android and iOS in popularity. But, I feel a lot of people may switch from Android and iOS if there are more affordable high quality phones with a good alternative mobile OS which is compatible with most apps, games, and services which most people want to use.
There are probably many millions of people worldwide without a smartphone or basic cell phone, and may buy an alternative smartphone which isn't using Android or iOS if the price is affordable for the phone, and it has the features they want.