This is a commonly asked question and nobody at all across the whole web seems to know! I agree that it would be nice to have it worldwide, and to keep growing I presume eventually Yahoo will bring it across the pond. But as for when....who knows?
I have not actually heard of this type of question lately. I had heard more about it in the middle of last year. I don't think no body knows. The best thing to do is to forget about it and only worry about joining it and getting accepted when it actually comes to your country, when that will be I don't know, but hopefully it will be sometime in my lifetime.
Last rumour I heard was it was still US only. The quicker they roll it out globally the better - especially for folks who have been banned by AdSense!
The last I had heard was at the start of last year when people said it will be coming to the UK in the middle of last year and I don't think it ever did. Well I haven't heard of it yet and I am located in the UK