Nintendo says 20m. Have they set the bar too high in recent years? Most recent one I remember is 3DS' first or second fiscal year.
Anyway, I'm guessing 23, since they usually lowball it. They have to have an Animal Crossing, Fire Emblem and Metroid or just a Pokemon to get those numbers.
20m is the shipment forecast for April 1st 2018 till March 31st 2019, not the consumer sales forecast.
No they're not going to sell 23m to consumers in 2018.
LTD Sales Predictions: PS4 - 130m, Switch - 110m, XBO - 52m
2019 Sales : PS4 - 15m, Switch - 18.8m, XBO - 4.8m
2020 Sales: Switch - 22m (Peak Year)