I think timetabling has always been the issue - if you have a load of services that go from A to B, then you introduce station C, do you simply replace all of those services with an A to C service? If so, what happens to all of the routes on the timetable that people have already completed? Do they just get removed? Or are they marked as complete, even though they have only been driven as far as B? The best solution to this is to plan extension from the very outset - the example I gave previously was my suggested WM Trains / Cross Country route. In that, you could build the initial pack with all of the local, EMU stopping services from Birmingham New Street down to Bromsgrove with the Redditch branch adding some variety. Then later on, you could extend down to Worcester/Malvern/Hereford and include the WM Trains DMUs on that route without affecting any of the existing timetables. There's also potential to extend further to Cheltenham or beyond and add on the Cross Country Voyagers/DMUs/HSTs that use the extended route. They all run the length of the existing line to Bromsgrove, supplementing, but not replacing the existing services, but where the original EMU services terminate, they continue onto the new extended rails.