I'm willing to speculate that the next generation of PowerPC processors will come in two flavors:
- 64-bit G5s without Altivec from IBM based on the Power4 design
- 32-bit G5s with Altivec from Motorola based on 90-nanometer technology
Wanna make a bet? <--- j/k
EDIT: To put it into perspective, splitting the chips between two companies is the way things have been done at Apple for years now, so this is probably the most likely thing to happen.