How about build that thing using the XPS 18 form factor with a 1.5 hour internal battery and put all the extra battery in a big power cover. When it's on the docking pedestal, it can be used as an all-in-one, and when it's being carried, users can make their own weight versus battery life trade off by their choice of which battery size in the power cover. With a hot swappable power cover, users who really want extra battery life could carry two or more of them. When I imagine this sort of thing, I think of the cover holding a removable wireless keyboard, swinging around about 285 degrees and connecting to a brace that hinges off the top of the back of the tablet, making a nice stable triangle.