This could be, in many cases implemented with firmware update, but I think that it will be only on enterprise models and not consumer/prosumer models. We can expect increase in processing complexity that a lot of devices will not be able to handle, also, manufacturers will have to apply for WPA3 certification, and this is not feasible from business standpoint. Another thing to consider would be that companies can release updates only to buyers with an active maintenance contract, or could limit themselfs to only newer devices, etc.
If you're building a new enviroment, can you wait whole year to get WPA3 certified devices? You can ask you manufacturer if they will give an assurance, but I would not expect them to do that for another half year.
If you have enviroment and you only need few new devices, can you wait and change all of them with certified later?