> I'm guessing this won't be a major problem. I don't know any proficient Rust or C++ developers that are not also proficient C developers.

There's a growing trend in high level languages like Ruby/Elixir/node to use Rust + FFI to optimize specific hot code paths. Likewise, pgrx is a much more approachable path towards postgres extension development.

All of these development paths have always been available with C, but Rust has made them more accessible to a wider range of developers. I'd wager a non-trivial number of Rust developers don't feel comfortable in C.