I'd be very surprised if they announce it in a Direct, as it would take too much attention away from the games (and vice versa). I'm expecting pretty much the same thing as the original Switch; a short video uploaded to YouTube to reveal the device, then a more in-depth look and game showcase at a later date.
To play devil's advocate, Nintendo has done one Nintendo Direct dedicated solely to new hardware in the past.I thought it was clarified that the person who posted this date was referring to the Direct date?