I am thinking more like Lua where you can create thousands of lua_State, and run them all independently with none of them messing up the global state of the app

I am thinking more like Lua where you can create thousands of lua_State, and run them all independently with none of them messing up the global state of the application. Something which is self-contained, portable, runs in a VM, doesn't use global state, whose execution can be controlled from the outside with hooks, etc. I don't know if ECL is disciplined enough to actually constraint itself in all these ways to be a good embedded citizen.