I do see the point you are making there.
On the other hand I also see a point about changing the rules during the game and so on.
If someone's been accumulating cash and intending to put it into the market whenever the next major downturn occurs or they switched their funds to a non-shares option or whatever then it seems rather unreasonable to change the rules half way through the game.
If the ASX is to be closed under given circumstances then what those circumstances are should be clearly stated prior to such a situation arising.
Also, all such markets should be closed at the same moment - so if the ASX shuts right now, and remains shut for a month, then a month from now the price of oil, gold, silver, all currencies etc remains at current levels. Physical trade continues for physical delivery but the price is locked globally for the duration.