Can you give some examples of Rust features that you don't need? Unfortunately a lot of common answers (the borrow checker, traits, move semantics) are things that are fundamental to the safety story. I guess one thing you could definitely subtract is async (Rust shipped without it after all).
I would keep lifetime generics, but remove traits and type generics (and therefore the really complex trait bounds, most of the GAT/RPITIT shenanigans, etc). I feel like that would remove most of the complexity, while leaving a mostly C-like language.
At most it should have pointer generics (similar to void* or Box<dyn Any>), where the generic function can't assume anything about the data, the data has to be heap-allocated, and the generic function can own and move the pointer around. Enough to implement collections, maybe iteration, and nothing else. Enough to not need monomorphization.
