
WHAT I'd wish for:
For a given train length (set in "Settings -> Interface -> Train visualiztation length"), make the last wagon visually distinguishable from every other wagon, IF it is shown.
To be clear: I'm talking about this "last" wagon, whose "wagon number == Train visualiztation length" (set in settings).
This is, how it looks at the moment (Train visualiztation length == 6):
And this, how i'd like it to look in the future (Train visualiztation length == 6):
WHY:
With this feature, a player will always be able to instantly see, if a track segment is long enough for the train length (s)he has set in the game options.
With this feature, if the last drawn wagon (visualization when holding signal and others) is not shown with the different color (or any other way the Devs can find), there is not enough space (yet) for your choosen train length, so you'll have to make more space. In this case, you'll notice the lack of space without counting wagons.
For example (Train visualiztation length == 6):
Here you will instantly know, your track segment is not long enough, because the "last" wagon is not shown in different style / color
I really hope, this description / depiction is understandable.

This proposal goes hand in hand with my other ideas about train visualization:
Train Visualization - Show Train Wagon Count / Index
Train Visualization - Visualize Train on all track segments in screenspace