I'm really wondering when did this Route du Sud talk start, because there's not any statement from Alberto himself, he never even mentioned this race.
A few days before the Giro, he said what he would do between giro-tour and that was barely spend like 3 days in Spain, maybe celebrating a bit if he wins then he would go back to Italy and isolate himself at altitude until the Tour.
That's all he said.
Riding Route du sud would be a really bad idea, it's not a proper training especially after Giro, he wouldn't need more race days. And he would expose himself to stupid crashes again in peloton or you never know with his bad luck recently.