I would look to another wall to add built in shelves. It would not look quite right in your configuration which right now is quite lovely. I had hoped for a similar thing in my lower walkout level. Even had the two flaming windows built high and wide like you see in a craftsman house…with built ins below…but my fireplace was flush. I put two furniture pieces there under the windows.

Thanks for the honest advise. I fear you might be right and is what I was afraid of.

Do you want the look or function? If your 'book' cases are thin enough you could get the look but not much but trinkets would fit on them.

I need look and function

From your photo the only thing I'd add on that fireplace wall is additional curtain panels.

Otherwise, it looks complete.