According to murrac, patches have been applied to Nautilus CVS to implement a tree view on a spatial view similar to what is possible with Aqua/Classic Finder. Judging from the screenshot this looks very similar to what xffm (and xftree in the Xfce3 days) did and still does if started with
xffm. Sure the UI looks cleaner than the default xffm UI, but at the core its the same concept. So, if that's what is needed to stop people complaining about the spatial Nautilus, why didn't they use xffm instead (probably even sending some patches to edscott to polish the default UI)?