Keeping up to date native Android/iOS functionality by basically reimplementing it bugs and all is an endless demanding work requiring strong talent that will never be good enough for all your use cases and will churn anyone who works on it both from the work itself and the constant complaints of the community.
No other programming powerhouse would be willing to partake in this or even be able to keep up - you won't see an AirBnB, Microsoft or Wix commitment like you did with React-Native, where these companies were active contributors to the core and have low-level libraries of their own.
Google is the last company I'll put my money for doing long term maintenance on an open source project, let alone one with no prospect for monetization or search market-share.
There's really only one way that Flutter survives - and that's if somehow Android moves to it as a first class citizen.
This is immensely unlikely. And probably will doom Android. And in the impossible case where it will - it means iOS will become second citizen.
