New carbon rim ring on Ferrari

There has been a lot going on about the carbon rings that were introduced by Ferrari. While it is allowed by the FIA as an aid to help cool the brakes, the dubious element has now evolved in such a way that hardly anyone could state it is not meant for reducing turbulence. The new ring is now larger than ever and seems to only have opening in the middle for wheel changes. Although Toro Rosso and Toyota adopted a ring too, it is surprising how few teams actually copy the device. Could they fear that developing it might make it illegal? Just like what happened with the mass dampers?