I personally wouldn't have any need for this because I use Gateway, but I'm assuming things like Pokemon Link (OR/AS demo uses it to transfer Pokemon to the full game, for instance) would use extdata. If this is the case, wouldn't a 3DSX homebrew be able to write to this, letting people import hacked Pokemon using nothing but Ninjhax?
EDIT: As I mentioned in my last post here, there's now a much better way to do this, so this thread is now irrelevant.
EDIT: As I mentioned in my last post here, there's now a much better way to do this, so this thread is now irrelevant.