Great suggestions! One nitpick:

But in principle I find this quite workable, as you get to write your CI code in Rust.

Having used xtask in the past, I’d say this is a downside. CI code is tedious enough to debug as it is, and slowing down the cycle by adding Rust compilation into the mix was a horrible experience. To add, CI is a unique environment where Rust’s focus on correctness isn’t very valuable, since it’s an isolated, project-specific environment anyway.

I’d rather use Deno or indeed just for that.