It is not clear to me, why it would be cheaper to ship the batteries separately. The car shipment might be theoretically cheaper, however it is much more difficult to ship cars which cannot drive. On the other side, you would have the increased risk for the battery shipment with the associated insurance costs. However, it is not obvious to me, that shipping electric cars is more risky. Actually all statistics point to electric cars being more safe than combustion engined cars.

As the article points out, it is probably necessary to change best practises of handling electric vs. combustion engined cars. Making really sure, that no car moves and crashes into others, change in firefighting strategies. Make sure, that the cars only contain a minimum amount of charge and of course continue to improve battery safety itself.

And you would not want to place the batteries densely together, in case of fire. Maybe put a few of them in some metal container or so, to keep them apart. Then one could put wheels on that container to move them more easily, maybe even add an engine.

"It is not clear to me, why it would be cheaper to ship the batteries separately. "

Special ships and specially trained and certified crews to savely handle de facto explosive equipment vs. totally hazzard proof expensive boxes of metal.

It might make sense to do this in big quantities. Probably will considered, after insurance companies raise rates after the first ship sank completely due to one carfire, that spread. Even with low charge they can burn out of itself. But sure, there are many other ways to deal with it.