First find a nice long buffet table you like, then go get your camera and go around town an take about 16 pictures of things of same subject matter, like, trees, or buildings or anything you think would make interesting picture in black and white, then go to someplace like Ikea and buy inexpensive picture frames (black wf white matts) and make a group hanging. Put a buffet lamp or two on the table with whatever else you love and you are done! You can always add cubes under buffet for storage and visual substance.

In addition, paint the vent the wall color.
Many things would work well: long table, large painting or quilt; really, lots things you could put there that would work.

What was there before the tree?

Wall of art.

How about filling the wall with built in bookcases? You could either DIY with one of the many IKEA-type hacks, or hire it out. Easily customizable and you would have a place not only for books but for anything else you want to display. And a book/display case wouldn't intrude on your passageway either.

I like the thought of a quilt on the wall and a long bench.

There are many things you can do with the wall, but a lot depends on what function you would like the space to serve

....a comfy love seat with bookcases and lamps on either side as a reading area

...a 2-man games table with a light over it for checkers, backgammon or chess

...2 smaller club chairs with a round table and lamp in between for reading

...a demilune table for display with a picture over it

...art gallery

...console table with lamps

...display shelves

....wallpaper panels

...piano or organ

...large shelf unit to be filled with traditional (glassware, plates, tchotchkes) or less traditional (mason jars, hats, shoes, whatever collection you may have0

Ikea Billy bookshelves -- only 11 inches deep! :)

Maybe two short Billy bookshelves in the middle -- and a tall one at each end ... large colorful artwork in the middle ....

Close the two shorter Billy bookshelves with doors -- very handy for stashing stuff (like Xmas decorations! :)

Bumblebeez - the vent is actually the wall color as of about 4 days ago. We had to replace the vent a few weeks ago & hadn't gotten to painting it yet, but it was on DH's to-do list for his vacation. :)

sasafras - nothing, it was a space I had put on the back burner. Actually that's not true, I have a (small) antique trunk that I had pushed there to get it out of the way. :O

cearbhail - floating, or anchored over a piece of furniture? (Art that I like is hard to come by - it may be a stretch to find a whole wall's worth but I'm certainly willing to try)

runninginplace - we had considered having our cabinet maker create a bookcase (not built-in though) that would match the cabinetry. I recently gave away most of my paper books (we're an e-reader family), but we have other things we could display in it. I wondered, though, since a bookshelf is going to be solid, and that back wall has that apothecary chest (with the lamp on it), and the sofa parallel to the archway has a sofa table, is it going to be like walking into "table, table, table" and seem too - tabley. :)

farmchic - interesting. I have displayed antique kilims on the wall but never a quilt. I like the bench idea, though - hadn't thought of that.

As for function of the space - I really don't have a desired function for it right now. I may not need it to be functional (I feel like I just broke a law!), I may just need it to be - inviting. The dining room is an office while our basement is being finished - it should be finished around summer (we're our own GCs). Once it's finished we will most likely use the dining room as a -- who knows what, sort of hybrid sitting/reading/relaxing room (with no TV). The basement will have a "home theater" room and a game area, wet bar, office, storage, full bath, and a bedroom/bonus room with walkout access.

Let me see if I can get a wider angle pic that shows the sofa table. I'd really like all of your input on whether or not I'm "room full of tables" if I do something like a console table, game table, or even the bookcase.

This morning DH suggested one of those ladder-style open/leaning bookshelves. Which he has mentioned before. So I should also say that we have a very rambunctious 4 y/o! :)

I like the leaning bookcase idea. Do you need a place to store and charge your ereaders? Maybe something like this from Crate and Barrel.

Or just three shelves in a row.

My favorite thing to do is try various pieces of furniture from your current home to test out the space. From a chair and a small accent table with a lamp to a console table with 2 lamps. Lean a piece of artwork on the console table too. Very quickly, you will find what does/does not work. Once the footprint is determined, you will have more confidence to shop.

I am opposed to anything like the ladder shelves because of dusting. In our house, it would become a catch all. Whenever I am composing, I think about different textures. A bench with a hanging quilt would be inviting, warm, and add texture. If you want simple go with a quilt, if you want functional go with a buffet.

You have a great point, lodalady!

I go through the same thing every after Christmas and buy something for the space and by the end of the year, I wonder why I have collected "so much stuff," and I store whatever and put up the tree, give stuff away and truth be told, put art on the wall and don't fill the space. Nature sometimes loves a void free of clutter.

A long table with art or a mirror above it would work.

OR