I think one piece, such as an armoire or wardrobe closet - would be good in that space.

I was looking at these recently. They have a few configuration options and lots of color choices. I‘m pretty sure the double closet would fit your space. But of course you need to measure. Depending on your measurements, the triple closet might be an option, too.

https://www.daals.com/products/oakham-double-wardrobe-shaded-white

I just read your post again and I see the measurements. The triple closet is over 57 inches wide so will not fit. The double closet will fit.

Get realistic about your storage. How many linear inches of books do you have, does your son have? How many inches wide and tall of board game boxes? Do you not have other spaces for books - yours and son's, and board games? This space is 27" deep. Bookshelves are less than half that depth. If this the best use of this generous storage space? If you have room for a bookcase elsewhere in your house, then I side with your wife about maxing this space out for closed door storage.

Have you considered having a double closet door installed there and then outfitting the space with shelving from Container Store or elsewhere?

Looks like a great spot for a built in closet organizing system that gives you exactly what you need.

The space is 53" wide x 27" deep; standard 8' ceiling.

This is nothing more than a 4 foot closet, not yet totally framed, and not yet having DOORS.

It is a CLOSET.. It is a simple trip online, and a trip to home Depot, a handy man framing and you give it to the Mrs.

Show the rest of your living spaces. Library books get returned to the library. There are lots of ways to store board games. We can't see the entirety of the loft, or any of the rest of the living spaces.

There are a thousand ways to customize a four foot closet......With DOORS: ) Please show the rest, including the sons bedroom.,... living room etc. We might see possibilities for storage you don't yet see.

Look into Elfa ..........And show us more, for more: )

But whatever you create could serve both of you. You can get a company like California closets to create storage options for you that perfectly fit the space. So that can be a certain amount of closed storage, bins, different depths for books and/or board games etc. I always put my library books on a shelf while I am waiting to read them too so I get why this would be needed. You can have it all be hind a closet door or you can have some of it open and some closed.