This doesn't really answer the question any it just adds more speculation in between again. But to rewrite the question with the new speculation - what made KaiOS able to succeed in starting without WhatsApp support and eventually getting it (last year) instead of failing on both counts like FirefoxOS did?
I.e. if you've got something to claim as the reason it can't also apply to KaiOS unless there was something KaiOS did right that Mozilla didn't.
