Cool project!
I was thinking that perhaps using wasm for the executables would address the security disadvantages. Processes couldn't snoop on whatever memory they wanted.
You could start with a wasm interpreter to get something running quickly, and then use a JIT later. Also an interpreter could stop after executing some number of instructions, so a process can't hang the OS (and a JIT could instrument loops to occasionally check for excessive runtime).
Just some thoughts. I also found this project https://github.com/kwast-os/kwast. Good luck!