I had this question as well.
Seems that it is rather cumbersome to swap the harddrive, not to mention that it's unclear yet if it might get you banned in the future. Response from Microsoft and their support was pretty clear: it violates their user agreement (you're not allowed to modified the XBox One), so I ended up buying a cheap Western Digital 2Tb USB 3.0 drive (like [http://amzn.to/1oIJ2qb|this one]) and am using that right now - works like a charm by the way.
After having bought that one, I did notice a possible more elegant option with [http://amzn.to/1oIJapM|this hard drive enclosure] which is said to attach nicely to the XBox One.
Not the answer I was looking for, but it is what I've decided to do ....
Hope this helps.