Simple fact is this generation will be the first (to my knowledge) not to outsell the previous one.
Thats a sad fact for any gamer.
I think:
Xone will be down although I couldn't estimate how bad yet
3DS will be down about 50%
Wii U and Vita will be massively down
PS4 has a good chance of being up but it has zero chance of being up enough to offset the drops above.