There are a couple I have in mind. Like many techies, I am a huge fan of RSS for content distribution and XMPP for federated communication.
The really niche one I like is S-expressions as a data format and configuration in place of json, yaml, toml, etc.
I am a big fan of Plaintext formats, although I wish markdown had a few more features like tables.
Most significant to least significant digit has a strict mathematical definition, that you don’t seem to be following, and applies to all numbers, not just numerical representations of dates.
And most importantly, the YYYY-MM-DD format is extensible into hh:mm:as too, within the same schema, out to the level of precision appropriate for the context. I can identify a specific year when the month doesn’t matter, a specific month when the day doesn’t matter, a specific day when the hour doesn’t matter, and on down to minutes, seconds, and decimal portions of seconds to whatever precision I’d like.
Ok, then I am sure we will all be using that very soon, because abstract mathematic definitions always map perfectly onto real world usage and needs.
It is not that I don’t follow the mathematic definition of significance, it is just invalid for the view and scope of the argument that I make.
YYYY-MM-DD is great for official documents but not for common use. People will always trade precision for ease of use, and that will never change. And in most cases the year is not relevant at all so people will omit it. Other big issue: People tend to write like they talk and (as far as I know) nobody says the year first. That’s exactly why we have DD-MM and MM-DD
YYYY-MM-DD will only work in enforced environments like official documents or workspaces, because everywhere else people will use shortcuts. And even the best mathematic definition of the world will not change that.