If the majority of computer users used the ISO dates, I would say enable by default. However, I doubt very much that most people know what ISO dates are or really care. Everybody sets up their o/s with the date and timestamp style that they are familiar with for the region that they are from. I, myself, don't use ISO dates and have no problem figuring out what month, day, year or time of day or night it is. Date and timestamp styles shown in file lists may differ from site to site, but I don't find that to be an issue. Those dates and times are usually irrelevant to the person going over the file list to begin with as it is the filename that is important.