Move the shelves all the way to the side walls and get an inexpensive TV console as wide as the space between the shelves.

For the molding we need to see the other walls in the room to see if there is a natural start/stop for the molding

Floorplan? More pix of other walls? Can't solve this one without seeing what other options you have.

I would hang the TV on the wall, get a larger console, and hang wood shelving on each side. I think that would fill the space better. I would definitely continue the crown.

Your shelving units are drawing attention to this area and not in a good way. Wallpaper will do the same thing. Remove both shelves and paint that wall a dark colour that goes with your other decor. Maybe even all 3 walls of the nook. Navy? Charcoal? Black? It would help if we could see the rest of the room. The TV and console will blend into the dark wall.

Don't worry about it looking empty without the shelves. It will look fine as you can see from these images, many of which show a very bare area around the TV. The dark colour is its own area of interest.

Consider assembling a wall that looks more like this one.

The way you have your things crowded into the middle of the space isn't helping. The bookshelves are not the right size for the space. Often we try to use what we had when we moved in, even if it isn't right for the new space.

I would start with mounting the TV on the wall, take the bookcases out completely, and see how it feels. If you feel you have to have bookcases there, get some that are 2 feet taller. Try putting the existing bookshelves (empty) on boxes, to give you an idea how it would look, before buying something new.

The dark colors are also a bit jarring in your space. Look for white or light wood colors to ease the contrast.