If someone wants to pay me to rewrite glibc in Rust, I'd gladly do it, as I'm sure lots of other devs would. It's actually something I've thought about doing as a hobby, but there are a million other hobbies above it on the list.
What we need is a way to coordinate the effort I suspect. Given we have glibc as a standard interface, a site which matched up function tests with implementations and made it obvious where to jump in could build a decent community.