May actually is not that bad of a time window.
Your point about having to announce it now is a bad idea because it would impact Switch sales for this holiday season and why would you want to do that.
May release means they can comfortably unveil say in January 2023 so as to not impact holiday sales and then launch a few months later.
I don't know if that's their plan, but a May launch is attractive for that reason especially.
I don't think again though "new hardware" means the "old hardware" is some how now obsolete. Nintendo probably ordered new hardware for 2023 years ago and it could simply be the hardware is ready for that time frame because these things have to be planned years in advance. If the don't want to leave the current Switch ecosystem they don't have to ... simply keep making games for the Switch OG and just let them run at 4K on the new system for several years before transitioning software support to the newer model.
I can see even Mario Kart 9 still being playable on the OG Switch because do you really want to lose out on a 100 million userbase. A 4K version of MK even with Switch 1 tier graphics is still going to look good.
I simply do not recall ever hearing of a hardware announcement and a launch a couple months later. Seems highly unlikely. Plus doing as such would be horrid for PR. You buy a $300 Switch for xmas to find out a week later there is going to be a better version...... yeah, brilliant marketing strategy. A great way to alienate a whole bunch of consumers.