I called it esoteric because there’s only a very small group of people that use ISO8601 dates the way you do so consistently inside notes. We used to have the date automatically remember the last format you used, which in your case would be exactly what you would want. However, in practice this feature meant that somebody experimenting with the format or not being fully aware of the way date formatting work, could then end up with a \date command that would not work at all, which affected a lot more people than what the feature was meant for in fact.
I think what could work is if we add a specific parameter such that you could force a certain date to become the default, for example, by typing \date(default-format: YYY-MM-dd) it would then use this format any time you type \date. I’ll try to get that in the next update.
Update: this is now part of Agenda 18 as documented here: Text Actions Cheat Sheet