I would say, chances are we won't see a new iMac this year, but I would wait until the other Macs gets released this year and see what apple does...I'm guessing they will tie it with the iPhone event unless a Apple Watch 2 is on the horizon (because the iPhone 7 doesnt seem to hold enough originality worthy of a focused event, ..based on the rumors that is.). If you dont see a new iMac then, I think its safe to say you are in for a long wait unless you get the current or a different computer.
Its going to be exciting, this will be the fall that decides if Im going to continue using Mac as my professional computer.