Internal power supplies in next gen consoles bother me. Let's take something built to be as small as possible making adequate air cooling difficult and stick the hottest part of it inside the case. Now granted, even when you don't have the power supply in the case, thing's can still be prone to overheating such as with the 360, or you can have them internal, produce a ton of heat, but be sturdy enough to take it like the PS3 usually was, but it just seems like a silly design choice to me.
Take them out, make the console smaller, cut down on the overall heat being produced inside the case, and make it much easier to cool so long as you haven't hired Microsoft engineers.