So, I have been playing around with the developer preview of OS X 10.10 Yosemite.
One of the first things I tried was to extract the ArtFile.bin, ArtFile200.bin and SArtFile.bin! To my surprise however they seem to only contain the old theme files, same as Mavericks! So it turns out that OS X Yosemite is storing it's theme somewhere else!
It's not looking good for Yosemite themes!
Some good news are that the dock is customisable again! At least in the current developer preview!
The image files for tabs in Safari and Finder are no longer located in respective resources folder!
New found 2:
After some research I found that the theme files appears to be stored as .car files in /System/Library/CoreServices/SystemAppearance.bundle/Contents/Resources
Never heard of .car files before but I found that they are a type of archived file similar to rar and zip etc. I haven't found a way to extract them though!