In my opinion, most TSW timetables are more than outdated due to the amount of vehicles showing up after release. Therefore, I think it should be possible to have a "wild card" option. If you mark it, the game lets you pick any vehicle for the drive. It also increases the realism because every train could have another vehicle type due to, for instance, a failure. In addition to that, we don't have to wait years for all timetables to get updated in order to drive our favourite trains on our favourite routes! It could get really exciting: BR 101 subbing for any ICE-train BR 103 subbing for the 101 BR 110 with n-wagen subbing for any RE or RB BR 111 or 182 subbing for any IC-train BR 403 subbing for the 411 on FFA BR 411 subbing for the 401 or 403 on KWG
Would only really work if that train ran on that route, during the period the route is set (perhaps with a little flexibility so as to not be too restrictive). For example, WCML layers on BCC, Glossop etc.