Thanks for the detailed description 
It was about it’s not possible to put the keyboard and spacers in all the connectors, so sure you can have a split keyboard but can’t use the middle connectors to put a spacer, since it’s I2C and not USB, nor you can swap the split keyboards (in case you want) since there’s no connectors in the correct place.
For full flexibility, I would have put USB connectors in the full row, both on keyboard and touchpad rows, allowing to put keyboard, numpad, spacers and touchpads however I want, for example a full row of spacers and no keyboard at all, or put the keyboard in the front row and second screen in the upper row, or a regular keyboard in the upper row and a piano keyboard in the lower one instead of a trackpad. Definitely that would have increased costs, at least for the materials of the connectors, but not doing it that way was shortsighned.