Interesting, but I think part of what made Classic Mac OS' spatial Finder work is that every folder only ever had a single window associated with it (similar to how in the physical world, spaces like folders and drawers only have a singular location) and opening a folder opens that window. It feels a touch strange to apply spatial logic to an Explorer-style navigator file manager.
I see. While making this I found that if you hide the Finder sidebar and toolbar (both are options in the menu), then your scenario plays out. In a way it’s nicer than the video on my github.
Yeah, single-window mode has been in the Finder for a very long time (wanna say since 10.1 or something), but compared to the OS 9 Finder it's always been a bit flaky and will sometimes forget window sizes+positions. I figure that it's probably never gotten the level of attention required to make it polished.
It's also missing the open folder indicator that the Classic Finder had, where folders that had their window open somewhere had a different icon (filled with a stipple pattern). This is a bigger problem than it sounds like, particularly with OS X having multiple desktops and making it easier to lose windows.