Ubuntu 25.10’s transition to using Rust Coreutils in place of GNU Coreutils has uncovered a few performance issues so far with the Rust version being slower than the C-based GNU Coreutils. Fortunately there still are a few weeks to go until Ubuntu 25.10 releases as stable and upstream developers are working to address these performance gaps.
You can fork, but I don’t think you can put a license on it because you are not the author.
You can fork it and GPL it just fine, the MIT licence allows for that, however anyone who wants to make the codebase proprietary can just fork the original upstream project. Not much point GPLing a project if you make zero changes to it. If you make changes then in practice just your changes are GPLed because anyone wanting to use code from upstream can just use it directly from upstream under MIT.