No, that's a good point.
It should only be one field, whether traditional GEDmatch or new Genesis. But perhaps with auto-recognition of which type was entered, the correct clickable URL could be produced, or perhaps no URL for Genesis ID's, for now. And perhaps a flag or appropriate note accompanying it. Then if and when GEDmatch changes/merges, WikiTree can adjust their handling as needed, with no user interaction needed, no WikiTree merging needed, just some page code to modify.