here's a list of suggestions under this:

current Train Wheel Assembly will remain untouched except for suggestion 2, 3 and 4

• More wheel configs (Single Axle and Tri-Axle)
• Being able to release train wheels from the rails (Preferably an On/Off Input so faster things like jet trains don't become basically unusable)
• ability to lock rotation (Useful for small shunters without having to use methods such as pivots moving blocks to press against the wheels which can cause physics issues.
• Occasional sounds of wheels going over track joints
• Sander dispenser and pump (offers better traction when dispensing sand over rails)
• More sizes (Small, Med, Large | useful for creating better steam locos or smaller trains like rail carts)
• Tilting variants
• Decreased traction in rain and snow (Sander can be used to neutralise)
• Volume setting for wheel slip squeel (my ear drums would thank you)
• wheels would be prone to derailing when damaged beyond a certain point

if you have anymore or feedback feel free to add them in the replies.