Well 2014 is the earliest PS4 will be released. 2015 seems good if they have best hardware by a good margin, like 50% performance over 720 as rumors suggest and yet affordable 499$. PS3 will be doing fine for 3-4yrs easily. This year is great with Ni Ko Kuni starting off.
I think when they release does not matter as long it is 50% powerful than the 720 and have good launch, start.







