I attached some examples for you to look at.

Photo 1 - thee mantle goes straight across and is more of a minimalist design, no siding.

Photo 2 - looks close to what you have going on already, the mantle protrudes a little to provide even more of a focal point. There's also a bit of detail in the mantle.

Photo 3 - In case you wanted to see how things could be if the mantle and bookshelf doesn't line up. The mantle is 3-sided but is also minimal.

Photo 4 - my favourite (minus the TV) this is a fantastic execution of a feature wall with the fireplace as the focal point. The mantle is full and beautiful.
Maybe the protruded wall might not be in the direction you are going in, but adding a stone mantle up the length of the wall could be a great solution.

Hope this helps!

Thank you. I wish I could do option 4 but its not going to work for me. I do like option 1. I truly appreciate your time.

I would suggest crown molding on top with fluted trim down the sides of the mantle to make it stand out more. You want the mantle to be a focal point. You could even build the mantle slightly deeper than the bookshelves to give it some dimension. Provided you stay within the limits of the fireplace specs.

Thank you. Good idea!