If a certification is awarded, which is true for both the Fibaro and Qubino devices, then it is a core tenet of Z-wave that any certified hubs (which includes SmartThings) will provide backwards compatibility to ensure that those devices continue to operate with hubs meeting any new Z-wave specifications.
This backwards compatibility is so important to the z-wave brand itself that they have even allowed older generation devices with less adequate security to continue operating if the customer chooses to do so, as explained in the second article I linked to above.
Most other network protocols would require that all devices be upgraded to the new specification, but Z-wave specifically has not. The example the Z wave alliance has always given from the beginning has been that customers should not have to replace their existing light switches just because they get a new hub running a newer generation.
If the devices had been using the “manufacturer custom code“ command classes, then that’s a different situation and other brands don’t have to provide support for that. But that’s not what happened here. They were using the standard multi channel commandset. They got through certification. At that point both device manufacturers and customers are supposed to be able to rely on the promise of backwards compatibility.
In this particular case, since the Zwave alliance did issue certifications for the Fibaro and Qubino devices, if there is a fault it would lie with the alliance itself. But almost certainly the resolution would be that hubs using the newer specifications be required to continue to support those certified devices. That is what has always been done in the past. Otherwise backwards compatibility would be meaningless.
(We saw an exactly parallel situation arise when direct association was changed for zwave plus. The way Fibaro used to use Zwave association is no longer allowed under the current specification, but that didn’t break anything for legacy devices. They are still supported using the old method.)