Good question and time will tell
The thing with the iMac is that the 21" models are still on broadwell, so you can make a case to bump them up, so both the 21" and 27" are on the latest chipset.
I wonder if they do the same with the MBP, would there be hue and cry about that action from recent customers?
That's true, they could just update the 21" iMac. I think if they dropped the price of the MacBook Pro it would help but first time adopters would probably be annoyed if there are updates already. As you say time will tell