I honestly don't see how they can ban them.
Whatever their home rules about such matters the WFTA core rules stipulate ANY clothes allowed, so if they have any contradictory rules they will surely have to be changed before the main event.
There are certain things that are left up to the National Governing Bodies of Host Nations but that isn't one of them. As I recollect South Africa had to make certain changes to their domestic rules to mesh with the WFTA core rules last January at their AGM.
"The Past is a Foreign Country, they do things differently there".