To start with it would be nice to have for example one standard DLSR camera model per camera manufecturer (e.g Nikon, Canon, etc.) with the same dimensions and the buttons on the same locations (standard means that the outside configuration should not change over say 5 years). With only the inside technology changing between manufecturers (camera brands) or depending on new technical developments. That indeed would be a noble goal. Because why would camera manufecturers take into account the wishes of people that put their cameras in UW housings?
Chances are the marketing types will say that if you change the outside 'look' you'll get more sales even on an incremental update. Most candidate cameras (at least 95%?) will never get near an UW housing.