What's their logic behind a Palutena reveal on that day? Is that the original release date in Japan or something?
Yes actually, 12/19/86 as what Wikipedia says.
My thought, as well as a few others, when considering that the 19th of this month, which is also a Thursday btw, happens to be the Kid Icarus anniversary which started on 12/19/86 in Japan (simply search "Kid Icarus Release Date" on google and check wikipedia). With that in mind, we're speculating something big involving the KI series to happen this Thursday, but most of us would think that it will be the reveal of Palutena.
However, considering how tomorrow will have the Nintendo Direct instead of Thursday, there's a chance that we still will get something KI related anyways due to time zones, and Japan usually being a day ahead of us sometimes (example being we're on Wednesday while they're on Thursday). Then again, being a day earlier wouldn't hurt.