Let's see, it's ahead of Mariokart 8 at this point in Japan, halfway what it was in Canada...
I'm going to guess first week globally will be around 400-600k.
The Wii U will probably last until 2017 before the next home console is launched (unveiled E3 2016, released 2017).
Splatoon has been bought by a huge amount of people despite there being little to do on it (I own it, for the record, and love the game), but all that free dlc they are releasing/will release is going to draw in new customers more than a typical game would get post launch. I think this game is going to have abnormal legs (even by Nintendo's standards) because of all the free dlc and advertising.
I'll say yes!