No quads.
There will bo no quads.
1) Apple has never, and will not, overshadow their pro line with another system. And again, what's the purpose of a rack server in the first place? Small, efficient, inexpensive, scalable.
2) A quad processor G4 would cost somewhere in the ballpark of $3,499 (if not much more) and offer the performance of rack servers costing half that.
3) The current revision of the G4 chip has questionable, if not downright unstable performance in anything higher than a 2 chip configuration. Motorolla has yet to bring the chips into full compatibility with multiprocessing standards, much to Apple's shagrin.