Rayon is known to have a higher overhead for the simple, and arguably most common case in numerical codes, static block size scheduling.
Things get better, and you start to benefit from rayon, as work gets less balanced.
Well, for one thing OpenMP is a c/c++ library, and chili and rayon are rust libraries.
It's probably possible to use openmp from rust, but the interface probably isn't as nice, you would need some kind of translation layer from rust closures and iterators to the OpenMP API
There’d definitely be some work translating Rust concepts over. It might be impossible/not worth it. But maybe it would be nice to have Rust, C, and Fortran all talking to the same runtime?
I guess they must have some really neat capabilities.