I noticed when I stopped manually on a bulk unloader that it removed the fuel from my locomotives. While you could fix it and call it a day, I think a filter similar to an inserter would be interesting. It would allow mixed cargo. I also managed to duplicate some bulk loaders by building them with construction robots. It only sometimes worked though.

Also, how should I space the loaders for vanilla wagons? My current setup is three spaces between the loaders but that's a little awkward.

Edit: Wow I just realized I posted this on the wrong page. I was looking for fast rail loader