That sentence doesn't make sense to me. If it's a gimmick then it's not here to stay. It has to be profitable to hang around. And people will quickly tire of it.
I suppose what I mean is that at the moment 3D is a gimmick on many films, however, when done correctly ie Avatar it is proven to be a very successful marketing tool and a draw for getting people to the cinema (like the film or not, it did do this). Those who have seen the film in 3D noted that it was far more subtle, adding depth to the screen, than was expected. This is the future of 3D rather than the 'pointy-thing-in-your-eye' moments of bad 3D efforts.
Plus James Cameron has long been a fan of 3D in films and developed 3D cameras with his brother for his Ghosts of the Abyss films. Whilst 3D has the backing of such hugely successful film makers it will continue to grow.
It has now become pretty standard for animated films to be released as 3D as these are by far the easiest films to 3Dify and I can not see that changing. Hence I feel that 3D is here to stay.