The main concern journalists and consumers need to be worried about as media ownership becomes more concentrated is accurate representation. This is always been a problem for media. There is a difficultly in representing the world the way it is actually built. White men have a tendency to dominate ownership, and therefore white men dominate the news coverage. I think it's important to make sure news coverage is as diversified as the areas they are covering. With the concentrated ownership becoming even more concentrated, it will be harder.
Certainly this has always been a concern for journalism professionals. But it should be a concern for consumers as well. They should realize that undifferentiated news rooms and coverage is news with bias and can't be trusted to the fullest extent.