I don't get it, and I don't have a dog in the C/C++ vs. Rust race. Ladybird has ~1200 contributors with a predominance of C++ contributions, followed by HTML, and with "other" lying at 0.5%.

That's a lot of people contributing.

How many of them will be less willing to contribute in the future, and less productive when they do if a sizable portion is in Rust? Maybe there'll be more contributions and maybe there'll be less. I don't know. If you've managed to develop a community of 1200 developers who are willing to advance the project why upset the applecart?