I am looking to design an extremely modular game engine that allows for portable native plugins similar to the way PNaCl works with chrome. The biggest factors I need would be: cross platform, sandboxed, and the ability to launch an arbitrary number of these plugins based on what folder they reside in. I can't have any internal code expecting a plugin to be there, all plugins will be added and will attach to my own custom API.
Is it possible to use PNaCl for this purpose and if not what is a good alternative?
Research so far: I know I PNaCl is portable and secure (sandboxed) but I still don't know if I can load a compiled PNaCl based on if it resides in a folder. I haven't seen any examples of it used outside of google chrome and don't know if it can be separated.