Placeholder dates always default to December 30th, you'll see that with a ton of other games available for pre-order without official release dates (Kingdom Hearts 3, Final Fantasy XV, etc.) that just means it's expected soon enough to pre-order but the exact date isn't known. I kind of feel like it'll either be a November game or possibly even spring of next year, we're supposed to be getting big news in April's Corocoro but even with XY we had 10 months between announcement and release date.
I kind of have a gut feeling it'll either be November 19, November 26, or possibly even December 3 but that last one would be pushing it a bit.