...that they become emotionally invested in? Many artistic endeavors are becoming much like sports, where they yelling in the bleachers is overcoming the enjoyment of the game.
I think fan involvement is the stupidest shit I ever heard. If you don't like the ending to some property, shut up or make your own. Two choices, that's it. Don't rewrite it to be "better" based on what you want to see, that is selfish and ridiculous and an insult to the creator or creators. For example: see religion.