I'm pretty sure that something like Android would start out as the first users, as they are interested and it doesn't run on any architecture that lacks Rust.
There is no plans to bring it into the core of Linux.
That and Asahi Linux (which similarly only targets hardware with good Rust support). The developer who has been working on reverse engineering the Apple Silicon GPU seems to be very seriously considering writing the linux kernel driver in in Rust.
There is no plans to bring it into the core of Linux.