The use of strings in Rust's implementation is limited to the assembly template and the operand constraints. Functionally speaking, moving those out of strings

The use of strings in Rust's implementation is limited to the assembly template and the operand constraints. Functionally speaking, moving those out of strings gains you absolutely nothing and can make parsing more difficult. The important part, type system integration, is already there. Sizes must match, move and borrow checking still happens, etc. This avoids the typical failure modes of unix-like stringly-typed systems. In fact if you read the announcement and RFC, you'll see that this was a primary goal of the new design!