I downloaded the build and tried it out. It's notably faster and pages now render just as nicely as they do in OmniWeb. Not everything works (plug-ins and some CSS stuff gave me some trouble), but it is a peek at what Mozilla could be. Unfortunately, there's no indication that Mozilla 1.0 will follow this direction; it will still be a CFM-based non-ATSUI application.
If you'd like to check it out for yourself, you can download the Mach-O Mozilla build from the mac.com page of 'stevekstevek.' Make sure you download all three files and then read the README.rtf file for instructions on how to make it work.
It's a shame this won't make it into the 1.0 production tree for Mozilla; I guess that leaves Chimera as possibly the best bet for an anti-aliased, speedy, Mozilla-based browser at the moment. [edited]

