There are two ways in which the bookstore differed from the current implementation of hacker spaces; ad-hoc local usage (book browsing), and commercial activity (book buying).
The hacker spaces I've been too have all shared a common "mode" which is "bring your stuff and we'll work in the same room." The allure being the social aspects and the interactions with other people interested in your space. But that has two problems, generally "moving" your space from where you work to the hacker space (for small embedded projects that is really hard), and for software projects they aren't necessarily "shared" any better in a social context other than IRC.
Hence the idea of the 'hack wall' which would be some common infrastructure that everyone would be able to see and work with (from a distance on their computers) and a common understanding of the opportunity and constraints. My thesis is that this is what the jigsaw puzzle does as a party, anyone can share in working on it, skilled or unskilled. At a conference I attended there was a similar sort of idea with "craft sticks" (aka popsicle sticks) and hot glue guns, but I think the need to be "artsy" was intimidating some people.
In my imagination the wall would be constructed somewhat like sections in a garden railroad might be, where each square would have some standard requirements, like power on the corners, 3.3v data busses, RS-423 connections, and maybe a serial port. And you could put squares together using something like 80/20 extrusions, then jumper across to the "standard" connectors, and each square would have a page in a local gitlab server which described its makeup. So to talk to an inner square you would have to create interfaces from the outer squares (which might all have a RasPi on them) to get to the inner squares.