Unless something has changed in the background, civil certification doesn't really look at STOL .. ie the normal design standards still prevail.
STOL, as a fire-breathing animal, is a peculiarly military thing .. the military have protocols to manage the risks in a manner which would not be acceptable to the civil certification environment.
Now, as to just how Captain Bloggs might fly his STOL-advertised bird in the bush ... might be a different matter again ... just don't prang.