Whether you like Rust or not, it's questionable as to why Canonical would push this so much and do it in such a cavalier way.
Will this really make coreutils more secure? I doubt it, if anything there will be a river of new bugs.
So, again, why are they pushing Rust so much? Having Microsoft make Rust a 'Tier-1' language also doesn't bode well.
It removes a GPLv3 dependency that might stop some companies from adopting Ubuntu Core.
Canonical has been pushing its own agenda for ages, how many examples do you need?
Microsoft making Rust tier 1 is great, it means probably one day we get a VS proper support instead of VSCode only.
If you head off to Microsoft official blogs, you will find out that Microsoft already has tier 1 support for Java (ironically), Python and Go, besides the usual .NET languages and C++.