First of all thanks for a great game. I have had tons of fun getting stuck in mud with group of friends and I'm eagerly waiting to see what you plan to bring with MudRunner 2. Here is a list what me and my friends are hoping to see in the future, mostly about things that fustrate/bother us the most with the current game.
No ghost vehicles/trailer/logs. For logs even currently I don't understand why they are personal as they will collide with other trucks anyway, pretty much only things that they ignore are other players logs and cranes which feels really strange. Your truck could just check if it has enough logs on board and then clicking load up cargo despawns the logs and spawns cargo.
Currently you can also pretty much "cheat" by just leaving your truck so other players can drive through it and you can pretty much park anywhere. This maybe could be option for the host as with random players blocking roads with trucks could be one way to grief, but with friends I think that you should always try to avoid parking on a road etc. This could also allow me to flip my friends truck without needing him to come sit into his truck.
Sync lights, if other players have lights on I should be able to see those. This could be performance issues for weaker systems, but for this reason this also should be an option (show other players lights). Also particles (dust, dirt etc.) would be nice to have from all vehicles not just your own, but that's more graphical stuff and doesn't affect gameplay like the lights would.
Gives us other game modes (multiplayer) and different objectives. You can do much more with those trucks than just transport lumber from A to B. Need new ideas? Just ask your community, I bet there are tons of great ideas that could be added fairly easily. Easiest ones would be just different types of materials that needs to be transported like shipping container from some warehouses yard to train station that requires different kind of trailer and crane (magnetic maybe?).
Challenges was a nice addition to new players, but with tons of mudrunning before those they were kinda lackluster especially as they were singleplayer only. Easy way to transform those to multiplayer directly would be giving an option to play those as friendly race. All players have the same challenges and objective in a small map like they are and then time how long it takes for each to complete given tasks. Also giving setting where you can either collide with others or everyone is a ghost to other and they can just see where you are going.
Challenges could have been also just added to normal maps. Like complete with only 1 star starting vehicles, don't open any garages (make do with the vehicles/trailers you can find from the map), etc.
Bonus: Mud deformation sync. I'm a game developer myself and I this might have multitude of issues and might just be pretty much impossible feature to complete, but if you can achieve this it would be really awesome! Internet bandwidths are quite high nowdays for most players so it might not be an issue. One idea for this I might have is that the wouldn't actually sync the deformation, but generate it locally like it currently does just for all the vehicles that are in the game. This would most likely be pretty high impact on CPU, but well give it as on option.
TL;DR: No ghost vehicles/trailers/logs, everything in the world all the time. Sync lights and particles + other effects. Challenges with multiplayer mode and added optional challenges to normal maps. Bonus: Mud deformation is feasible, might be technically really difficult to achieve.
Thanks for reading, here is an example how to travel longer distances without using any gasoline and proof that B-66 mostly floats in water (We speak finnish, but no need to understand what we say to enjoy the video)
And before anyone asks, the map is called Longridge in Steam Workshop: