Yeah, I don't agree with anything you just said. VLC was free software from day one. FFmpeg was free software from day one. Linux was almost free software from day one (the license was stupid). GNOME was free software from day one. All of GNU was free software from day one. I've covered just a couple of things you probably use all the time.
This doesn't mean you can't work on a prototype before releasing it. Most projects do that. But asking free software developers to sign an NDA isn't going to work. They'll just go off and make a competing free software product.