I can't quite see why Rust would make it harder, it's always a breeze compared to working on C++ projects, especially as the project matures. The compiler catches a lot of issues early, which otherwise slow down C++ projects as they accumulate silently, because they should have fixed all warnings, should have used ASan, TSan, MSan, religiously, and should have agreed on a manageable subset of C++, ... but of course didn't.

But I think the power of legacy and a bigger community is not to be underestimated.