IMO their ambitious goal is to replace both Android and ChromeOS.

From https://fuchsia.googlesource.com/fuchsia/+/refs/heads/main/d...

> This document proposes a mechanism for running unmodified Linux programs on Fuchsia. The programs are run in a userspace process whose system interface is compatible with the Linux ABI. Rather than using the Linux kernel to implement this interface, we will implement the interface in a Fuchsia userspace program, called starnix. Largely, starnix will serve as a compatibility layer, translating requests from the Linux client program to the appropriate Fuchsia subsystem.

So they will be able to run unmodified Linux binaries which should allow for a smooth transition from Android/Linux.

I'm not even sure that they'll rebrand Android at that point, as kernel for users is invisible. My guess is they'll just replace Linux with Fuchsia.