Switch was unveiled in October 20 2016 (4.5 months before Switch came out), so I wouldn't say it's out of the question. What Nintendo could easily do is announce it/unveil it after Pokemon Scarlet and Violet come out. They could disclose higher resolution features and performance for it and botw 2 at that time point if needed or perhaps in January 2022. Perhaps even offer players a free or discounted upgrade if they already bought it on switch to be able to play digital on switch 2, or not. Either way, it won't matter in regards to game sales whether people buy it on switch or switch 2, mainly as long as the 1st party games are offered on switch 2 as well. If Scarlett/Violet runs at a stable 900-1080p 30fps on docked and 720p 30fps on handheld with the current graphics displayed, people will be satisfied.
I think the Switch will continue to sell fine through the holidays even with a Switch 2 announcement in October. The majority of people who would buy switch 2 are the core gamers who likely already have a switch. Not to mention we are looking at a price point of $400-450 for the Switch successor, so it's not something casuals will buy in mass droves off the bat. They could reduce the current switch models price as well, when the successor comes out with Botw 2, if they really wanted more sales. $300-325 for switch OLED and $250-275 for v2 models and $150-175 for lite.