No one can say when the SAM460 port will be ready, and an HD4XXX driver has not been mentioned.
It is not impossible, but the original work centered around the use of an X1300 video card.

If things remain evolutionary, we should see an R400 driver (for support of the X800XT video card in G5 Power macs), and eventually an R500 driver (for X1300 video cards in the SAM460 and for later support of the X1900GT).

Who is to say what 3.6 will include?
Until its released, unless its mentioned prior to that release, its all speculation.