Can anyone think of a reason why to do this? Apart from personal fun project, of course!
The Mac Finder is a hot mess and seems to get worse with every release.
The 964 different desktops available for Linux are in general a hodgepodge of slow impossible-to-use disasters. A notable exception is XFCE but it's a bit of a second-class citizen and even things in XFCE don't work well. (Example: network configuration, you need to be logged in as root to use this applet.)
Edit: I would like to point out that the Win2k desktop was blazing fast on a machine with 256MB of RAM. I can't get Debian to install on a machine with less than 512MB without complaining.