Haven't thought about it much -- my first thought would be that the solution in the blog post could be the right one for a small office where movement of the base isn't necessary, and for one on wheels you should just go buy from Double Robotics. Their product looks really nice.
If I had to build one that moves around, I'd start with investigating the Roomba API, with an aim to mount the iPad on a Roomba and expose remote control of the Roomba to the chatter. You wouldn't get as high off the ground as a Double robot without making the mount unstable, though!
