Update:
"Tabata-san mentioned that 10 million copies sold is a voluntary goal that the development team set for itself. It has nothing to do with actual sales expectations from the company, nor with profitability.
He also admitted that its probably an unrealistically high objective, but it has been mentioned as am indication that the team is aiming to the top with this game."
Source:
http://www.famitsu.com/news/201604/01102924.html
Good news at least because 10m seems unrealistic to me as well.