Underfloor induction sounds really interesting to me as a new track type. I think it would be quite nice if you could refit some locomotives for it through some research. Touching on that, I think it would be quite nice if there was some kind of research aspect to this game. Not in the sense that you could research new train locomotives / track types, but in an upgrade kind of thing.
I think it would be quite cool if there was a research aspect that would let you upgrade certain things on locomotives you use, like engine reliability, fuel capacity, braking power, that kind of stuff. What you can research could depend for example on how many locomotives of a certain type you use (or maybe the milage). Of course there could be track upgrades too in that corner like: heated track switches or a higher voltage on powered rails.
Another thing that I think would be quite cool would be a modern and fast version of this
http://norm.beesky.com/blog/IMG_0434.jpg
Maybe instead of just turning lateral, also go vertical to increase the amount of tracks?
Again just throwing some ideas out there 🙂