That idea is VERY wrong in my opinion. Many players (mostly old ones) are becoming bored by just playing the game without any additional challenges, so one of the cool ways of giving yourself additional difficulty and feeling of being an actuall good player is to do lategame stuff before you are supposed to do it.
Doing raven's nightmare in chapter 2 can be a very internesting challenge for someone who never tried to do it, completing it will also give that player a lot of satisfaction. Why would you take that away from him?
Idea of closing these areas before certain chapter only takes fun from the game, by not giving anything. If you feel like you shoudn't do it before chapter 3 then don't do it - everyone can make that rule for his own gameplay, no need to force anyone.
Maybe there could be an additional switch after clicking a new game on gothic difficluty that would allow player to decide if he wants to have early access or not.