I think you guys are spot on when it comes to some economical effects, but I doubt that this leads to airlines ordering a plane and then, two days before it will be delivered, rejecting the manufacturer.
That's not the type of business anyone needs and I'm pretty curious about the special Cargolux explanation.

One could image various influences there, from missed performance data to the change in direction of the Cargolux management over even 'out of money' there, but in a business where you sell multi 100 million Dollar planes, both sides may usually avoid such overhasty actions, especially when it comes to the PR event of the first delivery.

So whatever drove Cargolux, they did not make friends at Boeing with this.
I think from the logistics, the Boeing guys can easily turn the current Cargolox plane into any other one, maybe switching some options, but the main impact happened on the PR side and leaves the observers somehow stunned with the current lack of information on why a deal was missed that close to 100%.

So lets see how this gets explained, mainly by Cargolux since Boeing did as promised so far, building the plane and organizing the delivery.