I love the fact Trains have entered ROR and since the first map is abandoed traintracks and train would be great.
I'm neutral about seeing trains as playable vehicles in the final game. However, I'd love to see them as part of the environment. In one of the MX vs. ATV games (I can't remember which), there was a train that ran throughout some of the maps. The train added an element of life to the map, as well as made an interesting obstacle. I would prefer if there was a non-controllable train running through the map. You could smash into it (or let it smash into you), race it, or try to jump over it in an orange Gavril Barstow. Worst commercial break timing!