For the uninformed, what problems would Rust's features and microkernel not protect against?

I can't even remember for Rust. I just know Rust team here admitted there was a cut-off point in terms of safety features it provides like any other language. For microkernels, all they do is memory isolation plus limit kernel-mode damage. Past that, you have to design extra capabilities into the microkernel, trusted code, or apps. You can even have concurrency errors in your apps with those if there's a shared-memory space allowed.