It isn't twice the size of microUSB, eyeballing it it looks more like just over 3 times the thickness. The thickness of the Thunderbolt/DisplayPort connector is over half the thickness of the iPad 2. You could only add a Thunderbolt port to a tablet the thickness of the iPad by letting the ThunderBolt port drive the case design (either by making at least one side flat, adding a large hump or some sort of fiddly fold down port).

I guess the x86 Surface will be a bit thicker than the ARM one, so I imagine that one would have space. But I wasn't really thinking about chunky x86 based devices when I was talking about tablets