A suggestion for added gameplay options is a pack containing various classes/types used on the Gatwick Express services since launch in the early 1980s. This could include... Class 73 and Mk2/DLV stock in various liveries. Class 460 EMU in GX livery. Class 442 EMU in GX livery.
The 460 and 73/488/489 is a bit too old for the current route, but the 442 is vaguely reasonable for the time period of the route. Although, there are other trains that would benefit the route more, like the 700 and 455.
I was thinking more of a special Gatwick Express pack which would stand alone from a general dlc which could include the types you mentioned. This special pack would be for players who like to see older stock on their routes instead of sticking specifically to accuracy in the time period.
A good suggestion. The older Gatwick Express stock would be great to have in a different timetable with older rolling stock suitable for their time period.