Probably early next year. Nintendo's console cycle periods usually run for 5 years (the GC and Wii life cycle were 5 years and Wii U was 4 years) so I'm expecting their next console to be the switch successor, not an upgrade version of the switch.
The Switch is on it's way to increase sales over 2020 in 2021 with keeping up with the momentum of last year and having a much beefier late year season than last year. Usually the next gen is started at least 2 years after the peak of the previous gen hardware. Nobody ever has brought the next gen amidst the peak of the last hardware.