I agree Mark. She did need a new appeal, this one show is not nearly enough to say if it's going to be a good change or not, but I think it will, she was a brunette before and I think this will be refreshing, in the end it all depends on the styling as much as it does on the color.
About Chanel, idk...it would be a bit strange that she didn't walk Chanel if she wasn't Givenchy exclusive, but as for the campaign, I don't think she ever was an option. Karl does that thing when he gets interested in a model for a little while, but his #1 fav and the one who has important roles in the rtw shows/campaigns always remains Freja. 
For some reason Natasha to me isn't really a Chanel girl. I think Fendi is a much better fit. Perfect actually.