According to a report, there is 30% of gamers on PS4 who never played The Last Of Us, so that makes 2,4M potential buyers(potential because not everyone will want to discover this game), not including those who want to rebuy it.
So my 1M prediction is the least to expect
Predictions for end of 2014 HW sales:
PS4: 17m XB1: 10m WiiU: 10m Vita: 10m