It's because it's not just a Let's Encrypt end-of-year message: it's an ISRG (Internet Security Research Group) end-of-year message. ISRG runs multiple projects

It's because it's not just a Let's Encrypt end-of-year message: it's an ISRG (Internet Security Research Group) end-of-year message. ISRG runs multiple projects, including both Let's Encrypt and Prossimo. Prossimo is all about using memory-safe languages to replace critical memory-unsafe code, and Prossimo funded a significant chunk of the work to get Rust into the Linux kernel.