I honestly don't see ToTK having a massive impact on hardware sales. It's a direct sequel to BoTW, so how many people who want to play it don't already own a Switch and a copy of BoTW? Maybe the 5 Wii U owners who haven't bought a Switch yet? There'll surely be some kind of bump, between people buying the special edition, and maybe some people who have sold their Switch in the intervening years or whatever. I don't see it being anywhere near "most of the units this year", though.
As a point of comparison, when Pokemon Scarlet and Violet launched last November, it was the fastest selling Nintendo title in history. It had very little impact on hardware sales, though. Almost every region saw hardware sales drop by about 25% YoY in the last quarter of 2022. In Japan, where we have week-by-week data, the bump was pretty modest, with hardware sales up 70K from the previous week, but still very much in line with typical sales for the same week in previous years.
As Switch reaches market saturation, the days of huge hardware sales figures when major games are released are long past. There's still a lot of people interested in buying Switch software, but almost all of them already own a Switch by this stage.
Exactly this, it won’t shift huge numbers of consoles but it will be the only title this year that could push more OG Switch sales and I think Nintendo know this. They’ll see Zelda as trying to ring out the last few sales they can from OG Switch before they then move their focus onto the future and Switch Next.