Yes but CSSU is not a newer OS and radically improved OS. It isn't a Meamo 8.1 developed on more recent & powerful phone and then adapted to older phone. CSSU is more like a iOS 3.1 or 3.5 (iPhone 3GS come out with iOS 3.0)
MeeGo/Nemo which is only the next step (like iOS 4.0) is already with reduced performance on N900