Honestly I think unsafe Rust is the solve here. Often you have an isolated data structure that is relatively simple that needs to break the borrow checker rules

Honestly I think unsafe Rust is the solve here. Often you have an isolated data structure that is relatively simple that needs to break the borrow checker rules (without invoking UB such as multiple mutable references). An often times a safe API can be written on top of that. However the current state of this is absolutely terrible. A lot of work needs to be done to improve the development experience with this model if it is to be used effectively in this way.