You can be pretty certain that UPS and FedEx will be among the last to adopt this technology. They operate fleets of predominantly old aircraft designs that are in no way compatible with this new technology, and besides that they have a lot more lower-hanging fruit that they can utilize if they need to lower their costs.
I think you meant to say they won't be the first and I agree completely. The capex to replace their fleets will be magnitudes more than the cost savings from reducing flight crews.
And even looking past that, it would be an understatement to say that the FedEx and UPS pilots I meet at work live a pretty good life, significantly better than many passenger airline crews do. If FedEx and UPS really wanted to reduce staffing costs, then it would be so much simpler for them to start there. They haven't, which really shows that the company isn't interested in lowering staff costs.
I am not criticizing them, I congratulate the crews and the company on achieving that. I just don't see the cargo airlines being first-movers with this technology. You will find it on passenger planes long before it finds it way onto freighters. Just look at the 777, the most modern freighter currently in service. It was 15 years before that plane came out as a freighter. FedEx and UPS are currently building fleets of 767 freighters. Those things will last at least 20+ years and will never fly with a single pilot. My own employer does a bit of cargo flying for FedEx, and we have just started "modernizing" the fleet with "state-of-the-art" 737-400s.