jailhouse VS ethercat

You could run it inside something like jailhouse hypervisor (https://github.com/siemens/jailhouse) if you want to give it direct dedicated "baremetal" access to hardware. You could do this inside of a buildroot linux image. This would need a customized simulator.

Yes indeed, and Siemens even has their own hypervisor: https://github.com/siemens/jailhouse

Yeah, I think that is what something like https://www.toradex.com/computer-on-modules/apalis-arm-family/nxp-imx-8 is useful for, where it has a separate core. Or even on linux you can use isolcpus to get pseudo-isolation. There are also hardware hypervisors like Jailhouse (https://github.com/siemens/jailhouse) which can completely isolate hardware resources and I suppose might prevent the GPU from causing an issue with realtime task. But this definitely affects ease-of-use and probably requires a reduced feature set in the language (no dynamic allocations) and lots of unsafe code.

Not directly related but there are some Rust wrappers around EthetCAT libraries such as https://github.com/ethercat-rs/ethercat. EtherCAT is commonly used as a realtime fieldbus in industrial motion control, for example KUKA and Staubli use EtherCAT between their motion controller and the servo drives. KUKA uses Acontis as the EthetCAT master software, but I am not sure what motion libraries they use.