There are just far too many variables involved for the flight crew to predict accurately the eta prior to being airborne. I tooka look at Flightradar historical arrival times for various routes over the past week and there was no pattern to many flights arrival times. Even when arriving into Dubai there may be straight in approaches, long STARs or holding. One would look a bit stupid having held at gate prior to departure only to be delayed at arrival. Surely it is better to have all pax on the ground, particularly as there are so many in transit, than to have them en-route & jeopardise connections. If the allocated gate is occupied, a bus from a remote gate would have the time to deposit them at the terminal close to scheduled arrival time. I can see this one backfiring soon, and a hasty notam to disregard will probably follow.