What Could Have Been: Simon was supposed to go evil in series one episode five, betraying the gang and forcing them to kill him at the end of the series, but the actor was so likable that it was rewritten.
Superhoodie was never intended to be Future!Simon at all. There used to be a video on E4's website of Simon filming a video and being confronted by Superhoodie during it. Superhoodie spoke in a different voice/accent to Simon and gives a cryptic warning about watching the gang before running off. Presumably the writers thought of the Future!Simon idea while writing Series 2 and just ran with it.