Rust goes a lot farther than academic languages that used regions like Cyclone or the ML Kit. In particular, Rust's regions are only used to enforce stack discipline, and the basic memory management is taken from C++. This way, we avoid the well-known limitations of "classical" region-based memory management.

Besides, consider the fact that we've written hundreds of thousands of code for working, non-toy projects in the language, including the Rust compiler, crates.io, Servo, etc.