The steam release notes say:
You may wonder what we do next. Still there is a large to-do list. One top priority issue is way points or at least line track selection at stations. Also, track construction should be more convenient. In addition there is a list of details like e.g. make cars waiting at railroad crossings. There will also be more performance optimization (especially for very large scenes) and finally, we also want to implement the widely requested vehicle auto replacement feature.
So:
-way points or at least station platform selection.
-Track Construction ease.
-Performance Optimization (still doesn’t play fluently for a lot of setups according to steam users)
-Vehicle Auto Replacement Feature
-Some small details like cars stopping at railway crossings.