More people using a PC, Tablet, Smartphone, and the many cheaper alternative consoles like Nvidia Shield, Ouya, iConsole, Madcatz Mojo, Gamepop, Gamepop Mini, Gamestick, iConsole, rumored Amazon and Google console, Onlive console, Moga Pro, Apple TV, Roku Games, etc could make the PS4 have fewer gamers since there are many regular and older people who just play games like Pac-Man, Tetris, Pong, Counter Strike, Angry Birds and Bejeweled and play games when they are bored, and don't care much about exclusives, story lines, and unique gameplay, so a cheaper $100-200 console or their current PC and laptop could be good enough for playing most of their favorite games.
I think the PS4 wouldn't fail, but have fewer gamers than the PS3 because of more gamers sticking to electronics they own like PC, Tablet, Smartphone, and cheaper alternative consoles than upgrading to a mainstream game console like the PS4.
Plus, many affordable $500 desktop PCs thesedays come with better video cards which are good enough for playing many games. If it is not, upgrading to a $100 video card like the Nvidia 650 can make it play many games on High video quality settings.
The multimedia features of next gen consoles don't seem very worth it since a Roku, Apple TV, and Google Android TV boxs can be bought for under $100, and they are good enough for playing Netflix, Hulu, YouTube, etc while also using less electricity, and making less noise because they are fanless.