libriscv looks amazing but its's much larger. It says "Less than 40kB total memory usage".
My first version (unpublished) of uvm32 was called uvm80 and emulated a Zilog Z80 CPU. My aim is to have a safe, embeddable sandbox for any device, rather than the best performance.
I'm working on an embeddable mini VM (RISC-V rather than WASM) and am considering this. In my model, there's something akin to a hardware watchdog where the VM is considered hung if it executes too many instructions without calling a yield() function in the host, then there's the ability to set a maximum number of instructions to execute before returning to the caller.