But the message is not just "we will require Rust and here's the timeline (and some things may break)", it's also "I know what I'm going to break and it's your problem to fix it" (via the CC line) and ends in a passive-aggressive way (the phrase "Thank you for your understanding." is basically a polite way of saying "and fuck you too."). This gets people off-side, and makes it more likely they're going to throw up barriers rather than either do what you ask or find some other way to collaborate/achieve the ideal outcome.