Sadly Coke RARELY listens to outside ideas. Pepsi is the same way but a little more flexible. I also honestly don't think Coke would have another Vanilla soda since there is such a small market for that. Just look how long it took them to create Vanilla Coke.
Vanilla flavored tea sounds like a better idea in my opinion. Anything is possible though with the way the cola wars are going and stuff.
Yoo-hoo has had a vanilla flavor in the past, but it was not very successful. There is a guy at YH in New Jersey - the plant manager - who is always looking at new flavors. With their new ownership with deep pockets, I'm guessing that the Double Fudge is only the beginning.
And, if you are a chocolate enthusiast, Double Fudge is a great improvement over regular YH!