A new option will b occurred by the future, before yu playing the game yu pick on timetable mode: The Consist Option. Yu can drive a train by selecting a number of the train yu want. For example, yu want to drive southbound to Gatwick or Brighton on the BML, either 4, 8 or 12 car set.
I would like to suggest a feature to replace the train in timetable. For example, I chose the service on M9 and changed the train to let's say M3. The service is the same, the timetable is the same. I just chose a replacement to suit my taste.
The OP seems to be suggesting what we already have, where you can enter in free roam and spawn a consist of your choice on a free stretch of track, set the destination etc. The other possibility is they want what someone just suggested in another thread. When choosing your train from the Timetable, the ability to customise (within reason) the driven consist. Per my example in that thread, replace the Class 87 with a Class 47/4 for a run on WCMLoS.
for me it would be enough if I could see in timetable/service selection what kind of consist I am going to get, like on German routes where you drive an EMU/DMU, if you are going to get a single or double or triple unit... I prefer at least double units, so that would be nice if I knew before loading
