There were differences between the Fantasy and Dream so I expect a number of things. For example, I imagine at least one restaurant experience will be different. And probably some sort of adjustment to the pool options. And the flex space unlikely to include the incredibles thing but rather something different.
Will the layout change? Not likely. Will the adult area be significantly up-sized? Not likely. Will there be more regular retail and fewer bars? Not likely. Will things feel less narrow? Not likely.
IMHO, there are design-level flaws on these new ships and there's no way the Treasure fixes all the wrongs I and others have with the Wish.