Alton Towers won't ever move the park entrance. It would make no sense at all. First of all they would have to build the entrance and build a place for guests to buy merchandise. Moving it over to the area I between Gloomy Wood and Forbidden Valley would make no sense either as it would give a few crowd control issues.
Most theme parks are specifically designed so that all the larger, more popular rides are near the sides or the back of the park so as to spread the crowds out. Having the entrance near some of the parks most major rides would cause huge crowd problems.
And finally, what would happen to Towers Street? The classic entrance buildings up to the lawns and the towers up in the distance! What I like to call "The Alton Towers Experience" would be completely gone in place of an ill themed and located, problematic and costly entrance at the other end of the park. And one more thing, Cebeebies Land was built purposely near the entrance so that the young would not have to walk as far to the rides. Fancy making the parents drag there moaning children all the way through Gloomy Wood, Katanga Canyon, Mutiny Bay to Cebeebies Land. All these problems about moving the park entrance because of what? A faulty monorail which can easily be fixed at a much lower cost?
Alton Towers will definatley not be moving the entrance any time soon!