With the value of the dollar collapsing, the PS4 and Xbox 720 will not be as much of a graphical leap over the PS3 and 360 as those consoles were to their predecessors. The third party development studios would have to pay even more money to develop games for those consoles and how long do you think Sony and Microsoft's investors will tolerate the hemorraging of money in their video game divisions. One thing is for sure, Sony and Microsoft will not lose the amount of money they did this generation with their next generation. It is simply not economical.
The advent of the PS4 and Xbox 720 will one day be here, that is a certainty. However, if you want to know where the next genration battle is going to take place then look at portables and services, which include online retail and interactivity. The Vita and the 3DS will duke it out in a similar manner as the bigger home consoles, but for the first time in gaming history handhelds are going to overtake home consoles. How they do this is debatable, but look at how the gaming industry in Japan is moving towards handhelds and even the western gamer is turning to IOS devices for gaming.
I do see Sony revealing a tablet controller for the PS3 and maybe Microsoft doing the same with the 360. I do not expect a new console from them no early then late 2013 to 2014. The Wii U will have atleast a year to fight the PS3 and 360.
No analyst or crystal ball BS intended. Just my two cents.