The bookcase is now gone, a wall stands in its place. I pulled the shelves out of the bookcase, glued in two pieces of foamcore board to almost fill the hole, then spackled over the top. Spackle, sand, spackle, sand, spackle, sand, seal, sand, paint, sand, paint, sand, sand, sand, paint, sand again. All the sanding was a pain, but it was needed, and the results of my careful work show. There are a couple of spots on the corners where I purposefully left the plasterwork imperfect, because that's more realistic in an old house.
The only part that bothered me when I was done was the bottom right hand side, it dips in a bit...it was very tedious to work on the corner where it meets the dining room without ruining the wallpaper. Rather than try to build up the dip I built a hall table to the same height as the top of the dip then made a potted fern, whose fronds are draped just so, to disguise it. I made the tabletop the shape of half of an octagon, to continue that theme, which I've used in the tower windows and in the walls and parquet floor in the foyer.
I wanted the hall table to have four slender legs, but when all I could find were these two fat ones, left over from building the kitchen sink, I figured they'd do. Once I was done I stumbled across skinnier legs while looking for something else. Since the back of the table is attached to the wall and the feet aren't glued to the floor I may try to swap the legs, if the skinnier ones are tall enough.
I need to make pictures to hang on the wall above the table...I'm saving that for later, I plan to do the artwork for the whole house at the same time, since I want to put clear resin over the pictures.