As of Q1 2018, 23 million KaiOS devices were shipped. It stood second in terms of market share in India due to JioPhone(even ahead of iOS). It seems future Jio Phones would be Android, especially considering Google is now invested in Jio(It's an investor in KaiOS as well). Mozilla had recently signed a deal to develop the gecko engine for KaiOS further.
KaiOS team saw where Firefox OS would fit well and they brought it to fruition; Something I feel Mozilla could have pulled off too.