I'd really love to see the OS4 team release a version for the G5 Powermacs, even if its just an internal version to show what the X5000 can do alongside it once and for all. I know if or when MorphOS comes out for it things will be a bit better since we can compare how it runs on both systems, but I am interested in OS4 too and want a reason to spend this kind of money over just using a fast PC or my A4000T with a CSPPC in it before I do it.
Well you can run OS4.1 Final Edition with your CS PPC and a Radeon card, you will get some compositing support. Obviously OS4.1 FE on an X1000 (or X5000) is much more fluid...the latest RadeonHD driver makes it feel very smooth (and of course you get the eye candy effects). You can also run it in WinUAE, but with all the eye candy / compositing effects it's almost a different experience. Looks much better and obviously faster.
It just is a better overall experience on the faster / modern hardware.