Have you read the article? It's about the mitigation system (the heap sandbox) they have in place to limit the bugs in the JIT can inevitably generate, not about improving the security of the generated code.
Correct, Rust won't help with the JIT part. But it would help with the sandbox escape which is the 2nd exploit that has to be paired with a JIT exploit now. As they noted, these sandbox escapes are primarily dealing with trivial memory safety issues that Rust would just make impossible to begin with, thereby significantly raising the efficacy of the sandbox mechanism.
Correct, Rust won't help with the JIT part. But it would help with the sandbox escape which is the 2nd exploit that has to be paired with a JIT exploit now. As they noted, these sandbox escapes are primarily dealing with trivial memory safety issues that Rust would just make impossible to begin with, thereby significantly raising the efficacy of the sandbox mechanism.