There is a license for retail, PC, Xbox One, PS4.
There is a license for digital, GOG, Steam, PSN, Xbox Live, Origin.
Just because you have bought the PC retail game, doesn't mean you can now get GOG codes, Steam codes, PSN codes, Origin codes, ect.
Just because you have bought the PC retail game doesn't mean you can now get the Xbox One game and the PS4 game because you have a PC retail license.
PC retail license and the gog digital license is not the same license. You can't buy the PC retail game and just expect to get the digital GOG game. Please understand that. Because it seems that is where your issue lays. The GOG license is different to the Steam license which is different to the retail license.
Yes most PC games comes with a Steam license but now with The Witcher 3 that is different.
Selling of codes. If it's legal or not legal, people will still sell the codes or the retail game. I am already seeing people selling the Nvidia promotion code.
That is what happens when you give people two licenses, they will sell the one. The selling of codes or the game if they get the code, is very much real, for a lot of people. No codes should be in the retail PC box and you shouldn't expect it.
Then you mentioned piracy. Piracy is what is known as your non buying audience. If you focus too much on people who will not be buying your products and you forget about the people who actually buys your products or if you make it hard and unpleasant for them, then people who buys your product will stop buying your products.
The gaming industry is moving away from focus on us buyers to focus on non buyers and it's going to bite them in the arse.
Now, studies have found out that consumers who part take in pirated media such as movies and video games, they buy more movies and video games than those consumers who don't part take in pirated media such as movies and video games.
What does this mean for The Witcher 3. The Witcher 3 is going to see really high piracy numbers, not because there are more people wanting to pirate the game because of DRM-FREE but because most of the pirate circle is going to want to download the game. As you said it's not just some indie game. So concerning the piracy scene, it is important that The Witcher 3 gets high numbers of piracy because it will lead to more sales.
At best Piracy is free advertising. I know The Witcher 3 is going to get high piracy numbers, much more than Witcher 2 got. And I do believe that if The Witcher 3 is a good game, which it should be, in other games, if The Witcher 3 is worth buying and these pirates (non buying) gets to play the game and see how good it is, it will lead to more sales. Studies can confirm this.
So don't be scared of the pirates. If you a good product such as The Witcher 3, pirates are going to buy the game, at some point at least. If you play video games and you get your hands onto something good that was pirated, you will want to buy it and own it. Pirated media is not owning a product. The Witcher 3, you going to want to own it. Well if it's good at least.
The Witcher 3, you just going to want to own it. So if you must have a back-up copy, buy the digital version / license.