Yes, we're actively working on adding this functionality to WebKit.
We're also working with the CSS Working Group in the W3C. It's not an either-or issue. Part of pursuing a standard is coming up with multiple implementations that show the standard works. So our work in WebKit is directly applicable to the W3C process.
We'd like have our code running in WebKit as quickly as possible, but we also want to make sure we're living up to WebKit standards. Our first few WebKit patches will be small (just adding the new properties to begin with, not actually doing anything with them) to make sure we're doing everything correctly. If all goes well you'll see Regions and Exclusions in a real browser soon, but we can't pin down what "soon" actually amounts to yet.
Well thank you for your fast answer. I must admit that link to the mailing list is quite interesting! I do hope also to see this implementation up as quickly as possible, but indeed everything should be done correctly. I had never actually imagined how big a project webkit was, and how difficult it must be to keep all that code working! I wish you the best luck!