[AlotOfReading]

Filter-branch / subtree doesn't let you move files outside the subdirectory, as far as I'm aware. Happy to be corrected on this point though.

[js2]

There's basically nothing you can't do with filter-branch and the variety of filters it can execute. Moving a subdirectory to the root is trivial with --subdirectory-filter, but even without that, you could do it with --index-filter or --tree-filter.