Technically speaking that should be possible. But I don't have a good feeling about making "unstable on stable" too comfortable or even first-class on crates.io to be honest.
Quite fundamentally it seems wrong to me to encourage people to publish something inherently unstable.
The important insight I had today is that only the publishing aspect is problematic, building something unstable is not, or at least not as much.
And it's actually good to have a reasonably strong incentive not to publish unstable crates for the stable toolchain. Otherwise we would end up with a domino effect, where each crate switching to this "unstable" channel would increase the incentive for other crates to follow along.
Too many regular consumers of unstable features would also mean more friction in developing Rust and ultimately less new features per year. We should optimize the development process of Rust for a high throughput of features, which includes minimizing friction when changing/removing unstable features.
I think it is important to find a sweet spot with just enough feedback for the Rust team, but as little extra burden as possible.
Yes we will still have to wait 52 weeks until Christmas, but we will get more presents / year.