I've been wrong before, I wouldn't say most likely. Its possible, but most likely is being overly optimistic imoApple will do most likely a silent update for iGPU models to Skylake era including Iris Pro 580 before WWDC. Could be also that 27" 5k m380 model becomes iGPU only, because they're pretty equal, at least on paper.
What happens to dGPU models, let's see. Maybe Apple will reinvent iMac when macOS comes out next fall... who knows.