Design being one aspect, I don't think Apple would really give the option of 16GB of RAM in their portables. With Apple's mindset of how they view their lineup, they figure if you needed that much power, the user would be better off with a desktop. Of course there would be others who say otherwise. Back to the design aspect of it, typically the more power, the more heat that's going to be generating. I could only imagine if you really needed 16GB of RAM, you're really pushing your computer to do something and that's obviously going tax the CPU and with Apple's design being slim, I really don't think that would be ideal. At least not for the upcoming update.