As we're embracing the off-the-rails era of TSW2's scenario planner, and with more preserved locos and routes coming down the line, I think it would be a good idea to introduce some generic coaching stock; for example BR Mark 3 coaches, or a set of Talgo coaches, that can be attached to any loco. They wouldn't necessarily have to form part of a specific new or existing route or scenario, just be available to buy and use in the scenario planner, attached to the loco of your choice. I think it is in theory a relatively simple way to make better use of the scenario planner. It would help create more opportunities for scenarios as well as liveries, particularly as not all routes are going to have empty stock lying around in sidings even if you can currently choose the loco and hook it up to whatever is available.
I like this a lot, it could be used with for example the upcoming loco addons for the koln-aachen route. I would like to see the 'Metropolitan' DB Rolling stock in game, plus some IC coaches of various different types. Then I could use the consist editor to have a Doppelstockwagen driving car, a mix of IC and metropolitan stuff on the back, and a br 187 to push it all.