From the new trailer I have seen, it shows jill and chris running together from a wave of water, shooting zombies, and walking together thru the halls. I am sure it will have co-op. this game is going to be so good :D lol.
If anything from the trailer, it implies Chris and Jill are NOT working together this time. My guess is it will be similar to RE1, where the characters are in the same area, but only occasionally meeting each other.