So every step forward leads to other problems. Vanilla Minecraft has no problem with a map evolving from major versions to major versions. The fact that mods break this should be made clear when downloading any FTB mod pack. If I knew that, I would have hesitated before entering into the world of mods. Most mods require some resources and an infrastructure to play with them. If every upgrade requires starting from scratch, there is little point in having complex mods because you spend all the time building the infrastructure (power supply, sorting system, ae network, taumcraft research), and end up finding out you lack a resource to play with bees, to craft some magic item, etc., and have to restart from scratch again to use the upgraded mod pack.