Don't mistake company politics between ChromeOS, Android and Fuchsia business units, and the technical possibility of actually bothering to do so.
Also don't forget Fuchsia has been mostly a way to keep valuable engineers at Google as retention project.
They haven't been trying to replace anything as such, and Linux kernel on Android even has userspace drivers with stable ABI for Java and C++, Rust on the kernel, all features upstream will never get.
Or on Rust's case, Google didn't bother with the drama, they decided to include it, and that was it.
Also don't forget Fuchsia has been mostly a way to keep valuable engineers at Google as retention project.
They haven't been trying to replace anything as such, and Linux kernel on Android even has userspace drivers with stable ABI for Java and C++, Rust on the kernel, all features upstream will never get.
Or on Rust's case, Google didn't bother with the drama, they decided to include it, and that was it.