A real useful OS in rust? I think this is a complicated question. I don’t see a rust based posix kernel ever taking off in an interesting way, the C based kernels are stable and fairly safe, the community quickly fixes issues when they come up. A new kernel won’t have the architecture and driver support so it will have those downsides with the upside being maybe more safety which is harder to measure. It’s just that compelling. Now a new hypervisor? Maybe some sort of unikernel core? Maybe some sort of container hosting microkernel or some new thing I’m not dreaming up right now? I could see that taking off. I think it would have to be a new thing.