I thought I just saw on another thread that one of the changes on the 19' 2017 is that the dinette is going to be raised. Is that true and would that also be the case for the u-dinette?
No, not in the normal layout (dinette in front). The rear floor area will be raised (like the 17') which will be noticeable as a raised floor area in the rear dinette if you buy the reversed (bed in front / dinette in rear) floorplan of the 19'.
U-shaped or regular dinette won't change the situation regarding the raised floor.