Good things come to those who wait This is why you shouldnt buy at launch; the kinks get worked out, its cheaper, and there are actually games to play on it.
Except if everyone had that opinion it would no longer be true as the console would flop and be discontinued.
I doubt either the Xbox One or PS4 will have big issues as they do not run that hot. Once you factor in their size I doubt inside the case is significantly hotter than Wii U, as their cooling abilities are proportionately better.
You will notice especially on the PS4, everything cools through the RF shielding of the console as well as the main heatsink. They also had the sense to put the HDD effectively outside the main console, so that should run cool too.