It's only a matter of time before the Linux kernel itself is rewritten in Rust. Or, more likely, a Rust-based replacement is written.
If starting over from scratch could you ignore most architectures, drivers, etc and support current hardware ... also yes.
A new OS could skip 32 bit mode, alpha, mips, itanium, loongarch, 68k, pa-risc, powerpc, s390, superH, sparc, parallel ports, serial ports, supporting zillions of PCI/PCIe cards that you can't buy any more, messing around with archaic 16 bit bootloaders, etc.
I am fully Team Rust for core infrastructure, but I am curious how many security blunders in the kernel are memory errors vs bad security architecture.