You know, perhaps the developers of the mod pack should try to develop a "world converter" - take a world save that was generated using the configurations of FTBBeta, and convert them to the ones that will use the new pack. There is already a program called mIDas that does it one at a time, so I don't see what would be wrong if the developers ask if it would be alright to create a FTB only version of the program.
Or, better yet, someone could just post the IDs that would need to be changed, and in what order, for safe conversion from one pack to another. Either way!