In fact, the shoe was not banned and it is one of the most widely used marathon racing shoes out there. Nearly all other running shoe companies followed suit and made more efficient racing flats with carbon plates and high energy return foams. Some restrictions did come out, including limits on the "stack height" racing shoes and more stringent restrictions on the track. The current generation of these, the alphafly 3, were just used to break a world record in the Chicago Marathon by Kelvin Kiptum. Those are unreleased as of yet.