"I want to point out one more time that the language doesn't require the GIL -- it's only the CPython virtual machine that has historically been unable to shed it."
http://morepypy.blogspot.com/2011/06/global-interpreter-lock...
Here are two examples of products that ship python. You can't just "swap out the interpreter".
http://www.thefoundry.co.uk/products/nuke/ http://usa.autodesk.com/maya/