I'm not sure when but I hope it's this year so people don't have to wait much longer to get a nice upgrade.
Possibly upgraded model may be pushed back to next year because it simply isn't needed at all this year, and Switch 2 is pushed back to like 2026.
At this point a Switch 2 coming out before 2025 would require the legendary sales "cliff" to appear, which doesn't seem at all likely, and even if it did that'd make a Switch 2 probably launch holiday 2024. 2026 successor is the most likely at this point.
Keep in mind they released the 3DS while the DS was still doing well. 2022 seeing just a slight decline from this year followed by the Switch 2 launching holiday 2023 would match that scenario pretty closely so very high Switch sales currently doesn't necessarily mean the successor is very far away. A holiday 2024 release date can happen even with sales still being pretty strong in 2023.