I love the suggestions of statement sized horizontal art. You don't need to fill the wall, just make it interesting. A suggestion for your fabulous new built-ins: if you can move those shelves around so they're at different heights. Not every shelf needs to be used. That way you can put something really tall in one of them.

First, take down all the photos, put "L" brackets on the bases of them and move them to table tops throughout your home. Place the bookcase on the wall left of the hall door and angle the purple chair and floor lamp out in front of it for a reading corner. Be sure it is full of hard cover books with something pretty sitting on top. Move the faux plant into its place in the right side corner of the fireplace and hang a piece of art centered 5' above the floor there. Add a mated piece on the left side at the same height. Adjust the sofa and end tables to be centered with the window if they aren't already. Pull the tables forward so they align with the fronts of the sofa arms and can be useful. I would get rid of the brown chair. Try a mirror and floating shelf on the wall beside the entry door.

I came up with an idea about an hour after I posted, but unfortunately Houzz won't let me delete or edit this post. I hesitate to do a runner here. It's fairly high traffic from the mudroom and I generally stay away from rugs (if there's an eensy teensy corner sticking up, I'll trip on it). But for the wall itself, I decided to take some black and white photos of landmarks around where I live and frame them. I have a couple usable pictures, and will go out and get some more (and better) shots. I'm not a professional photographer, but have taken a few courses and can get good shots for this purpose. Patricia, we have a long hall in our basement too, and that's probably where I'll do a few framed posters and family photos.

I think a couch that has less depth would work wonders in this space. You have a very narrow field to work with, albeit still doable. It might help to mount the TV, otherwise get a thinner console. Sectionals are usually unnecessary but if you plan to keep something similar, a sectional like this would work well. It has less bulk than your current couch and the sleek lines help to divide the room from the entrance.