Being pedantic, now, but it could be planned as a diversion airport assuming the diversion is made before closing - ie not from a g/a at destination. If a div is required to be nominated you would still need one that is available after g/a. The only advantage I can see there would be for nominating a suitable 'commercial' div. if, for example, destination went 'below limits' en route, but using a more 'fuel efficient' div for the g/a case. Bit of a paper exercise, really