I think polyglot causes more problems than it solves. It is gross how many different toolchains and package managers it now takes to build a distro. One person wants python, another wants node, another wants go, and now this. with node we traded buffer overflows for supply chain attacks. If they don’t want C, it would be better to start fresh. Robert Morris re-wrote enough of Linux in golang to be usable, and the overhead was something like 5-15% slower than C. If the goal is Rust everywhere, contribute to Redox. They are further along that road.
There needs to be a limit for each project. Debian is a large project so it needs to have more options than smaller projects. Rust is getting popular enough it is reasonable for Debian to say it is an approved option.
Note that I'm not saying Debian should, I'm saying it is reasonable that they would. I am not a Debian maintainer and so I should not have an opinion on what tools they use, only that adding Rust isn't unreasonable. It may be reasonable to take away a different tool to get Rust in - again this is something I should not have an opinion on but Debian maintainers should.
Unfortunately, the world is a complicated place and each one of these languages have their own benefits and tradeoffs that suit themselves to one particular language or another (ask an ML scientist to switch to raw C), leading to all of these languages having a valid place in the pantheon of softwares (except maybe for js). Since debian is a pragmatic OS, it needs to adapt to solve for the real problem of being generally usable, and thus supporting all of these languages. Rewriting Everything in one language would be a massive pain and likely a massive waste of time and supporting an OS with less reputation and stable footing like Redox would almost if not more counterproductive as rewriting everything in debian from scratch (it’s a bit hyperbolic to state the goal is to Rewrite Everything in rust), so supporting the gradual replacement of some mission critical components like the apt parser or whatever they’re talking about is likely more realistic. Although an OS definitely shouldn’t “move fast and break things” (especially not one like Debian) I don’t think it’s too ridiculous to drop support for architectures that can’t support a language that was released almost a decade ago. Having a proven language (I think it’s safe to say rust is proven by now, right?) that is much less prone to self-combustion on modification than C, yet maintains a directly compiled nature as well as being to interface relatively well with normal C libraries in some standard applications is a pretty good value-deal proposition in my opinion.
Applications vs Infrastructure: When stand-alone applications are in completely different languages, that is normal and reasonable and fine. When it takes 5-10 different programming languages just to build and manage the base system, that is an engineering failure and a mess.
Linux gave up the fight against complexity a couple of decades ago.