From my POV, Rust is already a bad decision for the same reason Linus was against C++. There's a continuous trade off against complexity and this is just such a huge addition to what was already a behemoth. I think Linus nowadays is a lot less strict in imposing his own rigor and engineering esthetics than he used to be.
It's probably been a long time since he was trying to steer the project to his standard of perfection, he gave up on that. Like he grew apart from it, life got in the way, and steering Linux is now more of a job than anything else.
What I'm saying is, 2004's Linus would have never allowed Rust into the kernel.
To begin with, there wasn’t really anything like Rust back in 2004, so it’s a very hypothetical scenario.
And since then, the world of tech has changed a lot. So I don’t thing it’s strange that Linux has also changed. All change is not good and that applies to Linux as well.
The Linux kernel has been a sprawling project from the start. AFAICT perfection and philosophical purity was never an aim of the project. This is sometimes a liability, but it’s also one of its greatest strengths.
For contrast, compare to FreeBSD. Much more coherent and from my POV more well-designed. But the pace of development is much much slower. Many FreeBSD users seem content with that. Which is fine! You can’t be all things to all people. But the user base is also a fraction of Linux’ user base.
So the fact that Linus is open to adding another language in addition to the 50-year old C language just seems to me like a good thing that can help to modernise Linux and Unix.
From my POV Rust seems like a good decision. Adding too many languages might become messy. And there are probably many many person-hours until Linux+Rust is mature and stable.
I think the jump from one to two was huge after development for over 20 years. I don't think there should be a jump or rush. Rust (while not necessary) will hopefully be able to eliminate memory errors and give better abstraction mechanisms in the codebase. If we have Rust and C, I don't see why we'd need another language any time soon. Those two should be able to carry the kernel by themselves. As far as I know, Rust is going to be for new drivers mostly, so they aren't going to be rewriting C code in Rust.
It's probably been a long time since he was trying to steer the project to his standard of perfection, he gave up on that. Like he grew apart from it, life got in the way, and steering Linux is now more of a job than anything else.
What I'm saying is, 2004's Linus would have never allowed Rust into the kernel.