We will get the next G4 bump in August, September or October. By October the 15" will be 11 months old, and as someone posted in another thread, Apple has never gone more than 11 months without an update.
Even if we get the new PB's Sept 1, that is only 4 months to MWSF. It is wishful thinking for such a huge update that quickly. Also, IBM getting the .09 970's to Apple in shipping quantities by then is extremely optimistic. The 19 watts someone quoted is for the .13 970. Apple will not use that.
I'm thinking the most likely time is WWDC 2004, either 11 months or 1 year after the g5 desktops were announced. MWNY is no longer, now Mac isn't even in the name anymore. This should be plenty of time for .09 970's to be plentiful, and the motherboards to be refined. This would also be 8-9 months after the pending PB update, which historically is just about right. (Another poster researched that the average time is 7.4 months)
Apple could bring out the dual 3Ghz PowerMac G5, and the single 2Ghz (I'm guessing optimistically) PowerBook G5 in one fell swoop.
On another note, I'm curious how many people would want apple to leave the 1" case for a 1.25 or 1.5" case, if it meant getting newer techologies in faster, like faster superdrive, 128Meg 9600 video card, G5 cpu, etc.