I have an analysis.
In order for Pokemon to be successful on the Switch, they should be targeting 8.21 million sales by September 2019, 90% of Super Mario Odyssey, the best selling game on the Switch. New core Pokemon games tend to have 90% of whatever is the best selling game on the system.
Remakes and remastering tend to get 75% of the a new generation game, so perhaps 6.15 million is a more realistic goal.
However, if Serebii's poll accurately represents the Pokemon fandom, 35% of people are disinterested in LGPE. 65% of 8.21 million is 5.33 million, which means this is what the final sales may be. Additionally, if
>>36944597 is accurate, LGPE will be receiving 70% of Splatoon 2's sales (7.47 million), which will be 5.23 million.
In the 3DS era, XY, the best selling Pokemon game on the 3DS, had 22% of the install base. The Switch has 22.86 million units. 22% of this is 5.03 million
Basically, if LGPE sells below 5 million by September 2019, it will be considered a failure for Pokemon standards.