PS4: Sony Playstation Graphics-Upgrade 2013
When there's going to a leap in the quality of graphics comparable to the leap of the SNES to N64, then yes - it is an appropriate time to introduce a new console.
When there is going to be an innovation in the way players use and interact with the console, like perhaps when the Wii introduced us to motion sensing (which of course seemed completely retarded and lame and not even fun to Sony fanboys during the Wii's premier... and then of course was rad when Sony came way too late to the party, and brought way too little with it's shitty Move controller. Yes, the WiiMote with the gay pinkpong ball on the end), or tried to integrate a hand-held console (Wii U, son) into the mix, then yes - is an appropriate time introduce a new console.
I'm not a nutrider for Nintendo or Microsoft or Sony or anyone really. I enjoy games on all consoles and on PC as well. The Wii was the last great console. I'm not talking about games here, fellas, I'm talking strictly about the console. Currently, motion sensing and the Wii U are what set Nintendo's console apart from playing a game on your computer. Yeah, Xbox and PS3 tried to jump into that arena too, but without as much success (to Microsoft's credit though, Kinect doesn't suck as hard as Move and the rumor is that they want to go further with the technology and create an entirely new gaming experience).
If you want to get a PS4 because of its specs, and because it's shiny and new... consider suping up your PC instead. If all you're looking for in a gaming experience is to sit in front of the screen, mash some buttons, and immerse yourself in fantasy and excitement, you can do that with a computer. And your graphics can be much better. I promise you, that on the day the PS4 is released, you will be able to build a personal computer that completely blows it away in respects to graphics, sound, and interface.
tl;dr - the PS4 doesn't offer gamers anything they can't get from a PC. Sony is not offering anything to the world of console gaming. Go play Diablo III on your computer. It came out almost a year ago.