Being able to put stock (of a different gauge) on special freight wagons.
Putting stock on freight wagons as if the freight wagons have real track on them. Its hard to put standard gauge on standard gauge but for smaller or larger gauges it can be interesting.

I think it would be nice to have this in the game, since the amount of narrow gauge is growing massively in the community. To bring standard and narrow gauge fans closer together I think this would be a great addition. This also allows for so called 'rollwagen', a system used in Europe where standard gauge freight wagons can be loaded on standard gauge, to cut loading times.

For the rollwagen system I would also like a way to actually drive the stock on, instead of only placing them.
I have already experimented with this concept, or I should say with the allining with the wagon and the track. placing both the track gauges on the same block height will have the SG lower than the rollwagen, having the SG track 1 block heigher will be too high. So I might also suggest being able to place track on half slabs. This can also improve making hills in general since you can make them more gradual.