Background: The author of this proposal, Daniel Micay (a.k.a. strcat, a.k.a. thestinger), is the most prolific volunteer contributor to the Rust compiler [1], and is fairly obsessed with eliminating design hazards that could lead to Rust not being competitive with C++ in terms of performance. For example, he was the driving force behind Rust's recent widespread switch from internal iterators to external iterators, and wrote most of the external iterator libraries himself.
EDIT: To whoever removed the [Rust-dev] annotation from the title of this submission, please put it back. It adds valuable context, and it's in the title of the page itself, so you're violating HN's naming policy by removing it.
Seeing a link to [mozilla.org] with talk about threading, I assumed it was something to do with Firefox (which I care about) versus Rust (which I don't).
But the M:N system is already written, and it seems as though it works extremely well. In fact, it is one of the things I like most about the language, and one of the reasons why I prefer it over C++ (as well as D and Nimrod for that matter).
This decision probably puts it closer to C++, but I can't see how that is a good thing.
[1] https://github.com/mozilla/rust/graphs/contributors
EDIT: To whoever removed the [Rust-dev] annotation from the title of this submission, please put it back. It adds valuable context, and it's in the title of the page itself, so you're violating HN's naming policy by removing it.