I voted late 2021. But, predicting Nintendo release dates is really just guessing. They sometimes announce stuff several years before release, and sometimes surprise us with big games coming soon. They also love to delay, delay, and delay again. So, I think the game will release sometime between today and the end of time.
Yeah it is just guessing. Really it's about trying to guess from what they showed how far away it is. They don't have a name, but they at least showed something which makes the situation less dire than Metroid Prime 4, and have assets and an engine to already work with, which we saw in the video. Some people just saw a logo for Metroid and thought it'd come out in 2018, look how that turned out.
They're not going to rush out a sequel to a game that saw universal critical acclaim, they want to follow that game up with something very special, and they'll take the time to do it.
Predictions (Made July 2019)
LTD: PS4 - 130m, Switch - 110m, XBO - 52m 2019 : PS4 - 15m, Switch - 18.8m, XBO - 4.8m 2020: Switch - 22m (Peak Year)