After having a look at the most recent patch for experimental (#101486), my overall experience was positive, however there are a few improvements I would like to suggest to improve the platforms visually, and improve the emersion of the rail systems currently in place:
1. stairs: putting this first because I think it will probably get fixed anyway but the stairs on empty platforms don't work, and one set on the main train station does not allow the player to pass through as they hit the structure above the stairs.
2. clearance: I believe that making the platforms smaller was a great idea, however two platforms cannot be placed side by side because of the clearance around the structure. This also means that the new smaller foundations cannot be placed alongside the platforms, always leaving space between the two structures. I think it would be better to tighten the clearance so that two platforms (one for each direction), or foundation(s) can be placed alongside each other so the player can walk from one to the other, making things look tidier and neater for those like myself trying to build more decorative bases, particularly the empty platforms which I feel would be used the most as a decorative feature.
one thing that could be added is a breaking / waiting system for points. What currently happens is that one train passes over a switch and goes in its assigned direction (eg left). Then another will come up behind and switch the points to the right for example (splitting the other train up and making it quite hard to collect the parts as they do not stop unless the assigned locomotive does). What could be done is a single like structure which will prevent multiple trains passing over a switch unless certain conditions are met
here is a simple version of how the state of the signal could be calculated (not sure how it could appear in game eg whether it will just spawn like the switches do, or whether it will require player intervention):
red (train(s) will be unable to pass through)
green (the current waiting train can pass)
train crossing the point
this could be used as a factor to avoid collisions (if ever added) on large junctions
switch is turned to same direction as the waiting train is going to travel
if the switch is facing the wrong direction, but there are no other trains on the junction, the signal could allow the train to pass. However if there is a train using it, then the waiting locomotive will have to wait for that train to pass (meaning that no splits will occur as train will not be able to change the switches state).
if it is switched in the correct direction, regardless of whether or not another train is passing, the waiting locomotive can pass
I know this would be quite complex to get working, however I think that something like this, preventing trains from changing points could fix a couple of the more annoying bugs /problems with the current experimental build. Trains could also just stop completely if this happens, allowing the player to replace the broken components. But this would likely happen a lot within complex rail networks, making it impractical. The simplest fix I can picture is to allow the state of the switch to be relative to the locomotive (if the current "ghostlike" style of train collisions is to be kept". A system like this would make switches less relevant, simply allowing the train to pass in its own assigned direction without the state of the switch needing to be changed (preventing breakups), however the switch could possibly still be used to redirect player controlled locomotives perhaps.
Finally, one small bug I noticed on the current build is that trains now do not seem to fully stop for long enough to be demolished, even on foundations. The trains also seem to 'slide' around a lot, but I think this I due to a current lack of breaking animation. I don't really have a solution for the aforementioned but thought it was worth mentioning, I guess allowing the player to break single locomotives if they are moving would be useful however I am not too sure.
To conclude: The game is still very fun to play, just suggesting a few ideas I think would improve the rail systems in the game. Hopefully this provides some inspiration for a better rail system if one is not already in development.