I suggest that there should be three control schemes, which the modeler can choose in the JSON file:

1. Separate brake, throttle, reverser. This is what there is in the latest test build, and should be the "default" (i.e. if the modeler hasn't selected a control scheme)
2. Combined brake and throttle, separate reverser. The throttle/brake is by default in the middle position (i.e. no brake or throttle). Moving it above the middle increases the throttle, whilst moving it below the middle increases the brake. The combined brake/throttle should be controllable using either 7/5/1 (brake controls) or 8/5/2 (throttle controls). This is useful for things like many British DMUs/EMUs.
3. Combined throttle and reverser, separate brake. The same as the old control scheme (before the test build). This is useful for small narrow gauge shunters.

If the config setting to use the old control scheme is enabled, then ALL locos use control scheme 3 regardless of which setting the modeler chose.

I don't know how to add the "Enhancement" tag to it