Rust will never be in Android user space, because it's not competing with Kotlin. Kotlin is already excellent there. Rust will replace the parts of Android written in C++ gradually. That was always the plan. It feels weird and cope-y to move the goalposts to say it's not a big deal unless Rust also replaces Kotlin.

Chrome only needs to replace the parts of their codebase that handle untrusted input with Rust to get substantial benefits. Like codec parsers. They don't need to rewrite everything, just the parts that need rewriting. The parts that are impossible to get right in C++, to the point where Chrome spins up separate processes to run that code.

Rust is the future for Android, and it will become an important of Chrome and Linux and git (starting 3.0). That's just the way it is.