Patrick, in your first paragraph you admit that there are breaking changes to Rust. Yet in your second paragraph you ask for evidence of the lack of stability? Your first paragraph provides the evidence that you're looking for!

Had I (or anyone else) written code a mere week ago using the old Chan and Port conventions, we'd already have to be updating our code. That's not stability.

I think it'll be safe to say that Rust is headed toward stability once you've committed to not making any more breaking language or library changes, you have a separate code branch receiving only fixes, there are releases available, and at least some assurance is given that any issues that do arise will at least be investigated for a reasonably long period of time.

Until we actually get at least one of those releases, I don't think we can consider Rust to be moving toward stability. We'll have to consider it a moving target, and we'll have to continue inquiring as to when it will start to stabilize.