The primary focus of the parcel fabric is it's ability to be both accurate and precise. Therefore emphasis on the coordinate locations of the parcel points with respect to the large amount of processing that the parcel editor tools do in the background make it extremely difficult to edit a fabric across a transformation. It may be available in the future, but as it stands now, it is recommended to project your data to what you'll be working with prior to loading to the fabric (IE Currently reprojecting a fabric is not supported.)