That's a wild leap with zero evidence. Fuchsia runs on one unimportant production device and has basically zero usage. Saying it will replace all of Android and ChromeOS is...optimistic to say the least.
> For more than two years, a small and stealthy group of engineers within Google has been working on software that they hope will eventually replace Android.
https://news.ycombinator.com/item?id=19702968
> "And while Android is reaching EOL in the next 4-5 years, most of this work will be carried on in Fuchsia OS, which is set to eventually replace Android"
I wouldn't bet on it. Sounds like IBM OS2 all over again.
General information suggests this is one of those long term things if successful would be massively game changing.