While I agree Cameron Toll might not be a particularly successful station, I don't quite follow what you mean with the examples of Gateway and Park Stations. Neither of these are justified by being close to the M8 or A720. Strictly speaking, Gateway isn't near a trunk road, but imagine you mean the busy Gogar roundabout from which you can only pick up or set down passengers. Both stations are close to employment centres, shopping centres, and on the tram line. Cameron Toll has shops, is near some university buildings, and maybe has a whiff of a tram line in many decades, so maybe some market can be perceived. However it seems quite difficult to contrive a useful passenger train service around the South Sub - it mirrors the loss-making 38 bus route.