The V6 Rav won't be available until Feb also. So an April RX350 is not too far off...

 

For the GS case, they didn't put the 3.5L in the new generation is because the upcoming 4.6L V8 is still in the pipeline. If they put the high-output 3.5L into the GS, assuming it will have the same hp like the IS, that will out-power the V8 GS430, which doesn't make sense. Even if they put the low-output 3.5L in there, with close to 270 hp, the hp number is too close to the 430, making very little value to the V8 model and hurting the "prestige" feeling of people buying V8.

For the RX case, it's probably due to the introduction of the RX400h. HP will be similar, and the new 3.5L V6 should have better fuel economy than the 3.3, and approaching closer to what the RX400h can achieve. Toyota is trying very hard to promote the advantage of the hybrid technology, and they are not going to use their own product to snap on their own face.