I can see only one viable path for Rust folks: Fork the kernel and make whatever mods are needed. It's not Linux anymore, but that's how Linux started from Unix all those years ago.
No, that's not how Linux started. No fork from Unix, if that's the comparison you were making. Linux started as a completely independent project, a multi-tasking kernel printing AAA...BBB, and, as it progressed, working towards being basically Unix compatible. But it was not a fork from anything.
Yes, my comment is poorly phrased, but the spirit is valid. Linux could not have come from Unix as Unix OSes were closed source at the time. It was not a fork. However, Linux was intended to be an open-source variant to Unix from inception. Torvalds aimed for POSIX and ABI compatibility from the start, it was one of his stated goals for developing the kernel.
I think that's not viable. To make that work you'd have to keep up with the kernel for years, probably more than a decade, to reach some kind of critical mass and become influential enough to be capable of separating from it and driving decisions that run counter to it. That's not even to mention the loss it would be to have these capable teams (rust proponents for the kernel and extremely experienced maintainers and contributors who want nothing to do with it) working in parallel at best and in partial opposition at worst, when they could work together.
This is much more of a manpower and money problem than it is a technical one. Of course it's possible to fork Linux and rewrite it in Rust. But who would spend all that time and energy doing that without the Linux foundations funds and expertise? You'd probably burn out within a few years before ever substantially converting the code base
What the Rust community is trying to do is antithetical to the whole free software movement. They want to impose a new language onto an existing body of maintainers who have limited incentives to change.
The "free" part in free software is not just free in beer, it's also free in freedom. That little bit gets forgotten. People work on it because they want to, not because they have to. If a developer does not want to use Rust, they can and should not be forced to. It does not matter if Rust is objectively safer, or better, or any of the purported arguments. Forcing it eliminates the freedom of choice.
The Rust folks should make their own kernel and OS. Let it compete directly with Linux. In open source, this is the way.
Since Con Kolivas resigned in 2007 there have been no volunteers making major contributions to the Linux kernel. Everybody is doing it as a job. So they are working on it because they have to, assuming they want to continue to get paid.