so you would have to assume that many of the discussed features will be going into Athlon 64 and Opteron.
No, one would assume that those features (different transistors, layout tweaks) are in *Low Power* mobile A64 and *Low Power* Opteron, but not in desktop varieties which need to clock higher, and can afford more power dissipation.
So what's the possible benefit of a different layout for Turion?
Making maximal use of transistor-based power savings tweaks often *requires* changing the layout.
What is AMD likely to gain that justifies the greater costs of new and future layout teams?
Lower power, more competitive mobile parts.