I've worked for airlines, many years ago, where during an RTO F40 was selected to give it a good chance of having been configured before the evac. Boeing then disapproved because it could cause a reduction in braking effectiveness. We asked why not passing 60kts, but the procedure was cancelled. When RTO was memory items including selecting F40 after park breake was set, there was not problem. Now, with it being a read & do, the F40 comes late in the procedure. It is only advised to wait for F40 if possible. I wonder if they have introduced a threat to a safe evac. I can see some pax opening the overwings before the call for EVAC and before F40 is set. In a Manchester type catastrophe I would not be surprised if that happened.