That's a cool dilemma! If this was my house I would fit a large board of upholstered tufted fabric in that spot, and fill the whole space. And I think I would make it the same white as your trim so it reads as a texture. Keep your existing headboard, it's neutral enough to compliment the tufting. Good luck!

Neutral grass cloth wallpaper.

I think it depends on what's showcased in your built-ins. You want the whole wall to feel balanced.

ETA: The blue square reminds me of the blue gilt-edged panel in Albert Hadley's apartment. Other decorators have used similar in their rooms. Have a look at this page to see if framing the blue might interest you. You could frame a piece of bold fabric or wallpaper as "art" in the middle.

I like the grass cloth idea.

The built-in shelves aren’t even filled but have mostly frames/pics on them. The built in across from the bed has a TV and more shelves.
Cabinets/drawers at base of all built-ins house clothes.

Looks like the space was meant for larger bed so I might add wall sconces to fill the space. These aren't the best but I like that they match the bed (right now the bed really stands out).

Any pointers on posting pics using my chromebook.....cannot pot anything tonight.

I really like the gilt framing of the blue square! The drawer knobs are glass/crystal with champagne gold necks do I think it will complement them. Even though the bed frame is dark gray metal and bedding is grays/blues, right?
Would it best to do this with thin molding (painted soft gold) so there’s dimension or could I even gilt paint a 1” border.
And a gilt framed piece in the center sounds good (just need to find something perfect).

Yes, you can mix metals. I'd do something with dimension, I think.

Susan Davis: can you try posting them to an ideabook and linking to that? The site is very glitchy today, particularly about pics.

One large piece of art would be super. The dappled light o the wall suggests that an abstract in soft colours would work well.

Tartanmeup, I took your advice and read the article about Albert Hadley. Loved the gilt frame idea and replicated it!

Still need to find the perfect something for the middle.

following

Wow, that looks fantastic, gargigg! What did you use for the gold colour?

I actually used a random pot of metallic paint I had lying around! I posted the transformation on Before and After too.
It’s subtle but I think lovely. My husband thought I was crazy but he likes it too!

A bigger bed can be accommodated but we recently moved in and with expenses adding up, opted to keep our old frame and mattress. I personally like the mix of the dark gray metal bed frame and the more traditional built ins. One day we will upgrade. I am looking for the perfect piece of art in the middle. I don’t want to rush it!