Well, it really depends on the creativity of the fans. In some 'Metal Gear Armstrong Crossover Fanfiction', they could rewrite the entire Metal Gear narrative with Armstrong as a central figure. He might bring his own set of abilities and motives, which could completely change the tone and direction of the story. For example, his superhuman strength and his somewhat unorthodox views could create chaos or order in the Metal Gear universe, depending on how the author wants to spin the story.