The same bugs will remain. AI drivers will still have weird faces and will ignore signals and track marks, and sometimes direction markers.
i-Portals will still be broken with a statement from N3V Devs saying they'll be getting to it at some point like all the other assets that stopped working when they've broken scripts without telling us ahead of time of the updates they made to the code.
The graphics though, will be stunning. The water will look like that from the Unreal Engine version 4.0, even though Unreal will be at version 300-something and be far more advanced. But... Trainz will finally have moving people like Cities Skylines following a real-life schedule with random traffic instead of cars that appear out of nowhere. The random traffic will cause rush hours at busy times of the day so that cars will gather around the stations as people actually walk on to the platforms and walk on and off the trains instead of teleporting. Note, the teleporting option will still exist for older systems and can be enabled in space-related traveling if people want that in their assets.
Trees will bend slightly in the wind instead of looking like they're in a gale, and we'll have rain and thunderstorms that rival the real weather complete with lightning and thunder instead of those sun showers we have now since T: ANE. Speaking of rain, this will puddle and pool, and create creeks and add to rivers, and may cause flooding.
The sky will have volumetric clouds and the whole weather system overall will be based on actual weather information from worldwide weather resources such as NOAA and other agencies in Europe, UK, Australia, Asia, and Canada.
Reflections and other volumetric lighting effects will work in real time since that will be standard with all graphics cards regardless of the platform. This will be the same with effects layers including grass and water layers. Speaking of which, we can just place a water layer and adjust it instead of fighting the clumsy interface as we do now.
Surveyor 20.1450 will still have the same Surveyor 2.0 interface but we'll finally be able to actually minimize the pallets without seeing the dark panel left on the screen. Classic Surveyor will still exist because many of the functions still won't be moved over.