That's what you do if you try to sell an "product idea".
Maybe he has been paying attention to the new fenomenon that is Internet. It's not amateur hour, it's innovation. Maybe he's been listening to the recent expert statements from Harvard and so on (maybe from Zittrain).
Point is to try to sell a product to the fanbase on internett. He uses the same procedure one does when aproaching companyes. One gives the synopsis and the synopsis
must contain the plot point, the ending, the twists.
This is not the business model of yesturday, it's what some people think is the business model of the future. Generativity. Look it up
If it's succesfull remains to be seen. But if you pay attention you would not ask if its amateur hour. You will se more people trying out the generativity way, pitching their ideas to the GA to use it as a "weapon".
If Millar is doing this because he actually listen to the Harvard-guys or just stumbled into this strategy I don't know. Maybe he's not doing the Apple routine, he's going for the Wikipedia strategy.
Point is, it's not stupid to reveal the ending if he wants to make the movie "Web 2.0"-wise. If he wants the fanbase with him all studies show you don't keep it locked and you don't keep secrets. Give them the synopsis
Just a thought. This is not the 90's