3D World and NSMBU have already sold tons (4.3 and 4.84 million by the end of June). I'm not saying Splatoon can't sell tons either because obviously it will (3.75-5 million depending on any crazy extremes that may happen), but if marketed the right way and bundled SMM should outsell at least one of them, if not be right on the tails of one.
I just can't see SMM doing any less than 5 million thinking about the other Mario numbers. I know it's different since there's no world map, but there's endless levels to be played and created. Realistically this should sell more than the other 2 games, but since it started later I'm not sure if it will, though I think it could :O
Like i said, Mario Maker can even sell 5/6 million for what i think, but only with those crazy sales can beat Splatoon!
Definitely agreed though.
Mario Maker has such huge potential, but since it is a first for this type of Mario game we can't say for sure if the sales would match the other games.
Personally I think it should sell better just because of what it is, but only time will tell!