PS4 - 85 million
Xbox One - 50 million
3DS - 75 million
Wii U - 22 million
Vita - 15 million
Shorter cycle, loss of non-hardcore gamers, intense competition for gamer time/dollars (LoL, Heartstone etc.). Handheld market under intense pressure from mobile.
To me, the biggest problem isn’t the hardware numbers, but the cost of development. We need huge install base to sell huge number of games (much bigger numbers than 7th gen) to offset the cost of development.