Monster Hunter World debuts with 1.35 million copies sold at launch, no digital included.
Above 2 million with Digital according to Famitsu
That is fine, but not great even great including digital. So the japanese base is more or less maintained. Lifetime sales will be strongly dependent on the legs, but that should be fine, it is MonHun after all.
FW and LT in Japan for previous titles:
MH Freedom Unite (PSP): 0.86M (4.13M LT)
MF Freedom 3 (PSP): 1.97M (4.87M)
MH4 (3DS): 1.78M (3.44M)
MHX (3DS): 1.49M (2.82M)
MH4G (3DS): 1.50M (2.63M)