Updated models with AMD graphics options expected in early 2017.
Apple Seeds Mac OS X 10.6.3 (Build 10D548)
There are said to be "no known issues" with the latest build, possibly indicating that we may be approaching release. 10.6.3 only began seeding to developers in early January but 10.6.2 saw a comparably short time frame from initial seeding to public release.
The Mac OS X 10.6.2 update was released on November 9th.