my own thoughts on it.
i think the main issue would be Residual sales of such vehicles, at present mainly a second hand motability car as a one owner vehicle has good standing and reputation within the second hand car market, due to be able to advertise it as one owner fully maintained ect, nobody knows once brought as the specs are the same as any other vehicle. Adding a “Disabled” Spec would confuse Joe Public and have a impact on resale prices. plus i agree it would result in less choice as manufactures would be less willing to discount other models, on more than one occasion ive heard sales staff stating a certain model is not on motability as a sales pitch for retail customers.