Currently Breeze notifications have a pretty squared-off look which, to my eye, doesn't match most other elements, such as the default rounded window decorations, buttons, and rounded borders. It would be nice if the notifications took on the same rounded corners for consistency and because it just looks better (again, to my eye).

+1

Strangely I think this use to be the case prior to Plasma 5.5; I'm not sure on what grounds the decision was made at that point.