There are A LOT of posts dedicated to this subject. Here is one that might be of particular interest to you. The people that know(apple) are not saying anything. The only people talking are making guesses. Bottom line is, only time will tell.
anything after mothers day to wwdc is the window. Imo before wwdc cause imac wont see a drastic change nor gains as many sellers as notebooks. so 3 tues wed chaces left in may. Each one failed brings us closer