It's not gonna happen this year (the announcement, that is).
Like
@oldpuck said already, there's evidence (eg: vgcharts) on how announcements/releases of next gen consoles affected sales of the previous gen.
This was the case with the DS -> 3DS, new 3DS -> switch. And before someone mentions how "the 3ds kept selling even after the switch's release" I honestly ask you to look at
how 3DS sales tanked ~1 year (more or less) after the switch's release.
And if you're thinking about the whole thing they had going with special ed. 3ds consoles released just a few months before the new 3ds reveal (which is kind of similar to the current situation we are in with the switch), I say don't worry too much about it.
That scenario isn't indicative of anything since back then I wasn't sure, but today I'm pretty confident that with the new 3ds, nintendo just wanted to make a definitive version of the console, not an iteration that brought
extensive software exclusivity or even a "next gen" device lineup.
Which looking at the OLED switch is... well, kind of the same idea if you think about it really.
January~March reveal with a launch in May~July is my bet.