I assume he meant creating an entirely non-ArmA based editor that read from map and mission files and wrote to the mission file. This would allow people to edit from machines that are too old to run ArmA or that wouldn't allow the installation of ArmA (e.g. an old laptop or a work machine).
Manipulating the mission file (.sqm), even when altering and writing it, should be trivial, since the format is a quite obvious text-based one, but the problem with the map file is that the format is closed and unavailable outside BIS. If someone has uncovered the format of that file and published it, then you should have no great problems using that information to generate a simplified map for yourself with a few drawing commands (openGL/DirectX if you want to do it properly). I'm not aware of this map format having been "cracked", but someone else might have this information available, if not already published. I know some people did manage to make map files before the tools were released, so I suppose there must be, at least, partial understanding of the file format out there..somewhere ;P