Have no idea why Merlin are doing this, but there are plans to move the London Dungeons to next to the eye. Rumours are it'll be for more purchases of the combi tickets as the eye, Sealife and the Dungeons will be in the same area.
All rides should be moved. I say that as I've heard that Extremis and the boat ride will be moved but haven't heard anything about Vengeance.
Official Plans: http://planning.lambeth.gov.uk/online-a ... MTDBOHV000
CF discussion: http://www.coasterforce.com/forums/view ... =3&t=34183