First thing: Gratulation for the successfull campaign.
It would be great to have both. The Beginning of trains in history and some futuristic stuff. espacially for the futuristic stuff the development part would be interesting. For all known present technology we all know what is relaiably or not, but if you can develope, as an example, underfloor induction for your trains as alternativ to normal powerlines and a new type of engine type (some field research for that from Bombardier is still running at Augsburg / Germany today), you dont know if it would be a good idea to update your train net with this new technic (maybe some unforseen problems will rise with some cows that crossing the track and will then produce magnetic milk ;), I think you know what I mean).
The gratest thing for me, would be, if it will become some day a full transport game, whit ships, Airplanes, helikopters, truck and something futuristic, not known yet. This would be open great oportunities for the gameplay if you have to combine the different types of transportation types like the are good for. But I can wait (wait since 10 years now ;)).
So keep up the good work and be carefull with the publisher 😉