I have made a model of the allowed bodywork based on the latest 2018 Technical Regulations, and it appears that the paragraph added to chapter 3.5.1 which attempts to eliminate the T-wing (and also the shark fin) still allows the possibility to have "mini T-wings" on the 2018 cars
The new paragraph reads:
c) When viewed from the side, no bodywork forward of the rear wheel centre line may lie above a line parallel to the diagonal boundary defined in a) and intersecting the rear wheel centre line 650mm above the reference plane.
Here it is: