As much as I love the idea of the woodburner and knotwork, that open space just begs to be a hidey hole. You could rig curtains and let him have Hide-n-seek space for now and a desk later.

I'd even consider painting the curtains to match a theme. Like do his whole room in Spaceships and find dark blue sheets and either sew or find the iron on patches in star shapes.

Something like that.

But then, I used to sit in my closet as a kid; I even put posters up and everything. I like hideyholes.