MFS and I were discussing this recently .. there used to be a requirement for a 10 percent penalty (accel-stop only, if my recollection is correct) in one of the design standards if there were no reversers. Unfortunately, neither of us was able to locate the requirement so it is a bit of a question mark still ... either way, I have no doubt that the FAA would be applying an appropriate additional conservatism (to replace the real world additional conservatism which they would see in the reversers) .. if the bird didn't have them.
It is one thing not to schedule reversers .. it is another not to have them available to the crew ...