I have a simple solution. Why not NDA people who are interested in doing development?

I don't think this is so much a licensing issue as one where people want access to the code to make improvements or bug fixes. If they're NDAed, they can get the source and hack all they want, but they can only share the changes with you guys, who can then integrate it into release images.

Or, have a seperate "Open" image, which the NDAed people can hack away on. You could then continue development of your internal software and the budding developers could have a seperate source stream to work on amongst themselves. No software gets out to the general public - you're happy. The hackers who agree to the NDA get source - they're happy.

Everyone's happy!