That looks really nice and I'm always looking for ways to increase our 2 BR CYV, only drawback I see is the finshed 36" door model at HD is about $1200 with tax. That's a little high.
Home Depot Bookcase Door
I did something similar to my home up north, if we had a basement here I would do it again. I had a 5' wide staircase to the basement and took away one foot and had a descending bookcase built the entire length of the stairway. My wife had over 75 cookie jars and it was perfect for displaying them. I had a carpenter build it for $1500 and then I did the painting and it came out very nice. At the top of the stairs where the bookcase ended and you had a landing and then a right turn up 2 steps to the main floor, on the end wall I hung a cork bulletin board and pinned photos to the board.