Logic would dictate that the new G4's that will debut at MWNY, will probably have these features:
1) CPU - Safe bet would be 1.0ghz, 1.2ghz, and 1.4 dual ghz on the top end. If Motorola has their stuff together we might see 1.6 on the top end. Moto has been demoing them, but who knows if the yields are good enough yet.
2) Now that the Xserve has DDR SDRAM, expect this to be in the new PowerMacs as well. Apple will probably bring DDR SDRAM to the L3 cache, as it did on the Xserve.
3) Will the Hypertransport bus make it in to this revision? Let's hope so, but since it didn't make it in to Xserve, this is iffy...
4) I'm sure Apple will stick with nVidia GF4 MX cards for most machines, with the BTO option for the GF4 Titanium. Let's hope Apple has the supply issues cleared up by then.
The only other big question is whether FireWire 2 will be included in this new G4. I'm betting that it will, since Apple sorely needs new technologies to drive it's professional sales, since lots of users have been hanging on to their towers for more than 2 years.