I hope we'd all standardize on the opposite: 2017-09-25.. it sorts properly when used in file and document names :-)
I'd also like metric time, but abolishing timezones and daylight saving would be more than good enough.
That is definitely also my preferred format, everything just sorts naturally then. Not so in love with the 2017-09-25T12:00 format as it does not work for filenames on my OS.
ISO8601 is very nice.
And you're right. I've seen some pretty strange stuff.
Sometimes, when forced to use ancient enterprise data systems, desperate staff use abandoned fields for new purposes.
I like American dates for sorting though :)
2017-09-25
2017-09-25-0929
2017-09-25-09290000000000