Given feet are unique and the general advise to have a good foot bed custom or otherwise I would expect all boot boards should be flat.
If the boot board is flat then those who choose a flat bed leaving the foot to function undisturbed can have this, while those who use an orthotic can do so without having to interface with a shaped boot board.
I have a relatively mobile and flat foot, I have used off the shelf foot beds, conformables all the way through to podiatrist prescribed full carbon and posted foot beds. I have boots with both flat and shaped boot boards and those that are shaped for me seem to do little but cause trouble trying to work around them and remove options for the customer
Is there a good reason that some boot boards are pre shaped or some advantage to them I am missings ?