Reading this article posted on the Times just now, I gotta go with banning any shoe with a carbon-fiber plate midsole. There are indicting comments in the article from George Hirsch and Ross Tucker amongst others, but I find Tucker's the most damning:
Embedded in the length of the midsole is a thin, stiff carbon-fiber plate that is scooped like a spoon. Imagined another way, it is somewhat curved like a blade. The plate is designed to reduce the amount of oxygen needed to run at a fast pace. It stores and releases energy with each stride and is meant to act as a kind of slingshot, or catapult, to propel runners forward.
Nike says that the carbon-fiber plate saves 4 percent of the energy needed to run at a given speed when compared with another of its popular racing shoes.
If accurate, said Tucker, the South African sports scientist, that is “the equivalent of running downhill at a fairly steep gradient†of 1 to 1.5 percent.
“That’s a massive difference,†he added.
https://www.nytimes.com/2017/03/08/sports/nikes-vivid-shoes-and-the-gray-area-of-performance-enhancement.html?_r=0
These shoes are providing aided performances in the marathon. There's no denying it.