I'm really not sure we'll even see a PS4. I thought I read that Sony was considering leaving the console market altogether, focusing instead on handhelds only.
I honestly am not sure I'd be sad to see them go...we generally buy consoles as soon as they come out (my husband and I both game and that's our big hobby), but we didn't get a PS3 until Metal Gear Solid 4 came out. We don't have a Vita yet and until I see a Shin Megami game or something I love as much, I don't see any reason to drop the money right now. The PSP almost never gets any playtime in our house. (It didn't see ANY playtime for a couple of years, then I got Persona 2: Innocent Sin and have been working on that.)
I know I'm a handheld gamer and that the DS/3DS is where most of my time/money goes. But the XBox gets time in our house, the Wii does just for 1st party titles, and the PS3 gets turned on when friends come over and they want to watch a movie.