I don't believe the G4 in the Mac would ever reach 2GHz. Given Motorola's -ness, I believe late Spring 2003 would bring us Power Macs up to [dual] ~1.5 GHz with G4s. That would be the final use of the G4 in the Power Mac. Late 2003 brings PowerPC 970 1.8GHz, keeping clock rates looking linear.
That's a good question, but I don't think that any answer here would be more than just hopeful speculation. Like you said, we all want to see it, but I doubt it will be with the G4.