Their first milestone is due later this year: to show the 2-way C++ interop.

Their second milestone should show memory safety features, and AFAIK it comes up a year or two later.

These milestones will produce technology demonstrators - so there's no expectations people would be using Carbon for anything beyond small demos and maybe check if it can be integrated with their existing C++ codebases.

Then they will try to package up the language and tooling around it with these two flagship features. This is where they expect some people to use the language for real. The language will only support a subset of C++ (they haven't decided what exactly it should include), and they mentioned Rust-like subdivision into "unsafe" and "safe" Carbon. To me this all looks like even after those milestones it may take a while.

Also, while Google folks are hopeful they also donated billions to Rust to improve C++ interoperability there, too. They don't bet on one language only but rather see multiple of them develop and spread.

So, tldr: it's years and years away.