My view on this all is something like this:

• Users should have their freedoms to use, change, share the program. Even if they are doing it for profit. Even if those users are corporations.
• Copyleft is useful to make it so when those who share, share, their versions of the same program is also Libre. It is not about protecting the developer. It is to insure the user still has the freedom.
• One is not required to share. So if I make a version of the program that works for me, I am under no obligation to give anyone a copy of it. ( But under copyleft, if I do, I need this copy to be libre )

So I can withhold giving away my copy until I get paid. Basically I don't even release anything until I get what I want from the deal. And I can do that for every change I make. But as soon as I make what I wan and release it, everything is libre from the beginning.

I can use screenshots or videos to prove that I have a working piece of software. And tease what are the changes I made.

The question now is, can there be a platform to streamline this process?