This just screams Sega Nomad to me, we saw how well THAT went over. Sony is not releasing a portable PS4, there are just too many factors working against it. Physical software would be a problem, digital only would cut the potential market for software sales. People still buy physical games, I cant imagine a portable console with a cd/dvd drive, would add significant bulk and cost to the product.
What would be the demographic for a portable PS4? Considering the PS4 is in year 5 with <80 million sold, are we expecting a large percentage of repeat buyers to put up $400-500 for a bulky portable version of something they already have. Are a there a plethora of new customers who havent yet purchased a PS4 who will finally dig in because now it's portable?
There's also the Nintendo factor, both times Sony has attempted a more powerful handheld than Nintendo they've come up short