Very cool work by the guys at Universitat Berne - Institut fur Informatik und angewandte Mathematick, and Andrew Black at OGI School of Science and Enginering, on a simpler, clearer way of providing mixin/multiple-inheritance benefits without their drawbacks.
There have been discussions on including Traits in 3.9. There have been no real arguments against inclusion of Traits, and many supporters. The intent is now to merge it in as soon as it is ready.
What is missing for Traits to be included?
Currently Traits can only be loaded into existing Squeak images through a problematic process that overrides various system methods, causing mysterious bugs. Since inclusion in the image these days means loading/merging as an MC package, there is some repackaging work to do. This is being worked on by SCG, Andrew Black and myself (Daniel Vainsencher), and we can't use help at the moment. However: