This is just speculation from a user of both Android and iOS and a developer for both platforms. It is my personal opinion and it might be completely off the mark.
I spent most of the day updating Learning Flutter. Google just released the first sneak peek of Project Fucshia[^1]. It's Google's new Open Source Operating System that might one day replace Android or Chrome OS. It also might not.
For now, it is just an experiment and no official news has been given on its future.
It seems clear that Google is spending a lot of time and money on the Fucshia making it unlikely to be just a gimmick. From there to say that it will surely replace Android in a short amount of time as someone is speculating is a fantasy. Google can't just decide one day to drop Android. It is going to require a large amount of time and resource to make the transition.
All that said I think it is for the good. With Oracle stake in Java and its approach in closing it ever further while requiring companies to pay them to use it, the whole Java ecosystem is in distress. There is still OpenJava (a still free and Open Source fork of Java), but having the key player on the market being so anti-consumer is not a great outlet to inspire any kind of confidence in Java's future as a language.
Google partially solved the problem by migrating to Kotlin on Android, but most of the code running the Android OS and SDK is still Java.
Apple is doing the same thing with Swift (for very different reasons) encouraging developers to drop Objective-C by providing Swift only frameworks. Internally though a lot of code is still Objective-C though and even though most of the new frameworks and code are written in Swift, the Objective-C part will remain there for a long time, if ever.
On the other hand, Google is known for shipping a lot of products to see what sticks and if they don't they get shut down just years later. One type of commitment is making an app (like Duo or Allo), a whole different scale is building an entire Operating System.
We'll get to know soon enough.
[^1]: Which weirdly enough didn't change the name. Usually, companies use code names for their product but change them for release (see Hummingbird that became Flutter for the Web or Marzipan that became Catalyst). This time the name stuck around.