A "floating" bookcase would be ideal while keep the spaces opened to each other.

Typically in a room like this your furniture and area rugs offer the demarcation in the rooms. Such as the back of a sofa or 2 chairs facing into the living room area. The only time I see a demarcation put up is if the styles of your living and dining room clash. Most people welcome the idea of shrinking and growing the dining room at will, dependent on the amount of dinner guests.

Actually, I did work on one combo that required a partial false wall to mount the TV. The room was narrow and there was a fireplace taking the wall.

I would simply use a sofa to delineate the two areas.

On the sofa idea, I think I would have a console table on the back of the sofa like these:
http://deciture.com/shop/furniture/7/studio-console-table/