It would be very, very difficult to certify a combi to the current regulations - note that all the combi's reference above were certified decades ago. The current regulations for fire protection, passenger/freight segregation, etc. make a combi cert far harder than it used to be. Hard to meet for new production aircraft - probably close to impossible for retrofit of an existing aircraft.
The linked article is short on details, but it doesn't sound like they are talking major structural mods (side cargo door and strengthened floor) - rather it's simply provisioning for a package freighter with hand-loading of the cargo (as others have already been doing with other passenger aircraft). Something that could be readily undone when/if the passenger market comes back.
An A380 Package Freighter conversion will still be handicapped by the A380's low MZFW, capping the total payload at about 85 tons - considerably less than the 777F (~100 tons) with far higher operational costs. Further, I don't even want to think about what the turn time of a A380PF would be with the main deck cargo hand loaded
. Probably a niche freighter aircraft at best.