It does not bring much if you think in the box, i.e. the top is RT, the base is Pro, and you use each accordingly.
Out of the box: what if the two parts can sync to each other in real time? How about they behave like a single machine? The Pro could display to your HD TV, or another something with a screen (kitchenware maybe). The RT can be a screen for anything with a keyboard (your TV remote). etc. etc.