Would be nice if ATC could close the arrival airport due to external conditions, like weather conditions that are beyond limits for safety (storms, blizzards, etc).
Would also be interesting to have some “random” events (of course with low propability), which would lead to closing the arrival airport for some time requiring a deviation to the alternate or holding (for instance accidents, computer outages, drone incidents, protets, etc.)
It would be realistic to have those on departures as well, but I guess in the context of the simulation it does not make sense (beside simulating ALL aspects of airline operations and finally beeing able to use the Delay Card of the Fenix properly)