If you write this date in ISO format, it's 40-4-6. And in hexadecimal, that works out to 0xfce.
So I hereby declare that day Xfce day! Let's start making festival preparations :).
Most every date I've seen written out numerically since the IBM PC days was written with six (or eight) digits. So it would be 40-04-06, wouldn't it? Or 2040-04-06 (around my locale, we'd use 04/06/40, and IIRC, in Europe and other non-US parts of the world, they'd write it something like 06/04/40 (I could be wrong)).
Not real sure that whatever date-writing convention is generally used will be so static that what will be used 26 years from now will be the same as what is used today, though.
BtW... You want to make a big deal out of "0xfce," lol? It's not a zero in my book, it's #1. So what date works out to be "XFCE1?" That'd probably be better if you're going to pick one single day for XFCE Day. IDK when it is, but I suspect I won't live that long - my friends tell me I'm in early middle age now; my body, though, keeps on insisting that I'm already an old fart (sins of a misspent youth ).