For Diesel Electric, you are simulating a generator-motor set, and properly modeling the set's performance at different throttle notches, as well as the way they respond to changes is challenging - but doable and with every Diesel Electric model made, DTG can learn from it. As for steam, to properly model it, you have to consider how much fuel is in the boiler, how much water, the temperature, the ambient temperature (if you get that detailed), the pressure, and then the flow. Is it increasing or decreasing? Then how much is there flowing into the pistons, the torque associated with the wheels, all of that. Then modeling the individual animations, gauges, plus modeling a fireman and such. Where most modern locos and trains are electrical, diesel, or a combo and the models are established. (ICE, motor models, etc), steam involves thermodynamic models which can be quite complex, and if it's wrong, it won't go over well with the community. I think steam would be cool, but it's something that will come later on once the income for the game is more sustainable and can afford to spend time developing. As for the whole "TS20xx has so many modern routes and it's nice to see older routes in TSW", I agree, and I get that argument. These routes though don't really push forward the development of the game though. I feel these routes are more recycling scenery and such. New trains, but that's about it. It would be nice to see a modern British route (fully electrified) just to have something different with EMUs along with longer range trains. I get we have GWE, but I feel TSW has come a lot further since then, and new developments might be cool to see. These routes in some degree appear simpler than more modern routes, but some variety in the DLC would be nice. My concern is that if the last few British routes were all throwback/older routes or heritage stuff, is American stuff going to go on a similar path and stay in the NYC area? I'm not against something like a NJT route with multilevels (they would be nice in TSW), but variety is nice.