Yep, Japan is at two million already, above Diamond and Pearl's 1,588,734, about the same as Sun and Moon's 1,905,107 first three days.
Guess all the doom and gloom early in the thread didn't align with reality.
Now that we have a Sword/Shield number including digital sales, an estimate for digital sales should be added where applicable when we compare Sword/Shield's 2m to the other games.
X/Y was released at a time when simultaneous physical + digital releases were still in their infancy on Nintendo consoles, Sun/Moon was better off, but I still wouldn't put its digital share above 10% because that's about the value where Switch started from in 2017.
Including an estimate for digital sales:
Black/White - ~2.6m
X/Y - ~2.2m
Sun/Moon - ~2.1m
Sword/Shield - ~2m
A decline is still there, but Sword/Shield's high digital share makes the decline considerably smaller than zorg1000's conservative estimate in the post linked above.