i don't think they'd put a G4 into the iBook until they release the G5...
why?
to keep the consumers and professionals apart
now, even though that brings the iMac into the fold, it's a consumer machine with a g4, i still think they'll wait. if you get the g4, you'll want more complex tasks, you'll need better graphics card and higher resolutions, something that would definitely raise the cost of their affordable portables.
once they release the G5's, the prices of G4's will go down, therfore making it more feesable for them to put a, say, 800MHz G4 iBook and a 1.2 GHz G4 in the iMac (or higher, considering how high the new G5's will max out on their first trip into the world)
well, that's my $.02