[dlfylwkt] Preserving data during repartition and reformat

Create a tool to repartition and reformat a disk yet preserve some or all of the information previously on it.  One imagines a UI which shows the old partitions mounted, the proposed new partitions, and a drag and drop of directories in the old to new locations in the new: perhaps things in the old get put into a subdirectory named "old" in the new.

Under the covers, the tool handles the monstrously hairy task of reading from partially destructed partitions (perhaps embedded inside encrypted volumes or LVM) and writing to not yet fully constructed or formatted new partitions.

This would be an improvement over the current practice of temporarily copying needed data to an external disk first.

I'd like to see this in a Linux installer, which often prefer a complete reinstall for each major new version.