A testament to the original Kentmere paper's longevity. Congrats. I have asked the same question myself both here and to Ilford directly on a tour about paper sizes. For instance most 5x7 sheets are used for 135 negs so 5 x7.5 is much better but I fear pigs will fly before such a size is produced.
Of course Ilford and other manufacturers will argue that with 4x5, 645,67 and 68, producing a better size may only be better for one size neg and there is logic in this. However I think there may be a case for 5x7.5 given the amount of prints this size and how much 35mm cameras are used in comparison to any other size.