Why is this an issue? Simply recompile and download each package. If the distro worries that the maintainers would take too low just fork and recompile the packages themselves. These days its really not that big of a problem in terms of disk space or network traffic. And if some packages are large its often because of images resources which can be packaged separately. It seems like a lot less effort then trying to guess if dynamicly linked library will work with every package in every case after the update.