Reasonably practical idea, but suffers the same flaws as a motorcycle sidecar. I don't know anyone who would be caught dead in the sidecar. So now its more just a place for your luggage, in which case a trailer is probably better for handling.
Also you'd be quite wide as a bike and would make it near impossible for vehicles to pass you on a single lane road. If you're on a double lane road, would you be brave enough to occupy the entire right lane? (I know in Vancouver you'd be risking your life to do so)