True. The best location of side and bottom keys vary greatly for different people. (Attached figure is just an example that shows the minimally needed key size and the exact optimal key location for one particular person -- me.)
In order to reduce the variation, a minimum 2u gap between the left and the right - hand halves must be added, and some keys must be made wider or higher (side and middle keys would be > 1u in height, at least two keys must be then relocated from side columns to middle columns, and bottom keys would be > 1u in width). What's worse, even with that, the key location must vary, or it won't be optimum for all people.
It is possible to make a single PCB that fits all reasonable variations of side / middle columns and bottom row in size and location (at least for some types of switch). For example, for the bottom row, a single PCB can fit all combinations of 1u, 1.25u, 1.5u in size, located anywhere in 0.125u grid, for up to five modifier keys on each hand side.
I wonder if it is possible to do so for the plate and the top cover.