Yes, it is a known thing. Look at Wikipedia: ISO 8601 or in a bit more entertaining way:
(Thanks to xkcd.com)
The reason I would not want to use TextExpander is that I dream of a possible mass export from Agenda into single files and do not want to handle every file individually, e.g. a journal of a vacation trip and then at home include that into my diary of single files that have just the date YYYY-MM-DD as names in my case.
But I use this date format plus a title also for every business note, minutes, and each and every file you can imagine.