My take on this is that subinterpreters by themselves don't excite me that much, but the possibility of having subinterpreters running each in their own thread that do not have to share a single GIL is a huge potential win for Python. No other popular language has the huge restriction on multi-threaded code that Python has with the GIL. I have been hoping for years that the Python dev team would recognize that as an issue and try to do something about it.