I don't think this would be a hard change to implement, programming-wise. Currently, when a route is designed to layer in a loco/MU from elsewhere, the specific loco is hard-coded at the time the layer was implemented (typically when the route was made). So, for example, in SKA the S-Bahn services layer in the 422 from Rhein-Ruhr Osten, because that was the almost-close-enough train that happened to exist at the time SKA was released. But then Munchen-Augsburg came out with the 423, the correct train for the Koln S-Bahn... however, even for HMA owners, SKA still features the incorrect 422. How hard would it be to rework the layering code so that the app checks the DLC database with an if-then-else routine? I.e. "if HMA found then layer in 423, else if RRO found then layer in 422?" (This would also apply in future to Riesa-Dresden, since apparently it will layer in the ICE3 as a placeholder for the correct ICE)
1) there is no such thing as the Koln S Bahn, Koln is situated in the Rhein Ruhr S-Bahn as it serves several major German cities including Koln, Dusseldorf, Dortmund and Essen and sees routes S6, 11, 12, 13 and 19 pass through Koln HBF 2) the 422 does operate on the Rhein Ruhr S-Bahn on S6 3) the HMA 423 would need an overhaul to run on the S13 and 19 lines we can run in game as the 423 for HMA as the name suggests is set up for the München S-Bahn and would not really be compatible with SKA as it would have none of the correct destinations, line numbers or even livery
1) No, Koln has its own S-Bahn run by KVB independent of the RRVV, in its own livery. 2) The S-Bahn lines that run out to Duren, the S12 and S19, use 423s. Only. Doesn't matter that 422s run on non-modeled parts of the network. 3) Not possible. Layered rolling stock is imported exactly like it is on its home route without change. Like it or lump it.
Did you read what I said at all? I literally said the ones on HMA are configured for the Munich S-Bahn (shocker), i literally said the livery on Rhein Ruhr 423s are different to the ones on the Munich S-Bahn
And if you read what I said, you would know that repainting layered rolling stock is impossible. You either get Munchen 423s, or no 423s at all.
I'd much rather have the right train with the wrong paint, than the wrong train entirely. Especially since you have to look pretty closely to notice the differences. Does it bother you that all the 146.2s in-game are registered to the Mannheim depot? By your rule, there would be no layering at all, since no train is marked correctly if transplanted from its home route. (Especially since I'm running my 422s in proper green RRVV livery, whereas Munchen 423s at least are red)