Quite agree Tim! Slight telephotos bring on their own set of issues where field curvature is concerned but I was restricting my comments mainly to wide-ultra wide angle lenses.
Although I'm familar with the issues of the Nikon 28mm f1.8G, the lens that I encountered to be notorious for displaying fairly extensive curvature was the medium format 35mm lens I mentioned previously. The curvature becomes more extreme at greater camera to subject distances and it's not until around f11 at mid distance subjects that the depth of field becomes significantly large enough to achieve good sharpness across the frame At subject-focusing distances close to infinity, even f16 leaves some residual evidence of the curvature and it's hard to achieve uniformity of sharpness across the frame of a field subject.
Of course as you pointed out, it can work in the photographers favor for cone shaped subjects. I was photographing a semi-circle reflecting pool (umbrella shaped) that was tree lines around it's perimeter. Even at f4.5, the entire semi circle of trees was sharp, edge to edge, which wouldn't have been possible if the trees were in a line, straight across.
It's well known in optical design that in wide and especially ultra wise angle lenses, especially those designed at a reasonable price point, that to increase sharpness in performance, curvature and distortion is the price one pays. Look at the 3rd party 14mm f1.2 lens (sold under various labels)....very sharp lens with tons of barrel distortion. Same goes for the quite good sharpness of the Nikon 16-35mm Vr lens at 16mm. They achieved good sharpness at the wide end by allowing distortion remain as part of the optical designed. There are many other examples that could be cited.
Dave (D&A)