The World Curling Federation has now made the information from the recent “Sweeping Summit” live and ready for public sharing: http://www.worldcurling.org/ss2016-update
The most interesting statement I found was "A single fabric from a single source should be used on all brushes approved for use at WCF Championships and events. The preferred fabric identified at the Sweeping Summit is a woven product with no external waterproof coating or artificial texturing." I'm not sure how this plays out in practice - do they issue approved broom heads?