One of the easiest ways to get into a place that has that open floor plan feel wihtout actually having to build something, you might be looking at a loft space. The problem there is, though, that you now have one giant open space, and while some may be able to live in a space like that, some would not. Enter PLI Architects They have a beautiful way of dividing space without constructing walls. One might think of the system as "residential cubicles" - only NICE.
Here are a couple of pictures: