I would like to see realistic steam trains added to RCTW. The option to choose the locomotive style, passenger car style, colors etc...
Steam trains like the one at Walt Disney World, Also the ones at some Six Flags parks, And some small style trains like the Canobie Lake Park: Canobie Express.
There needs to be an ability to have the peep paths cross the tracks using just the path material, or wooden planks in the track bed. Also have signals at the crossings for safety with the option to have gates at shorter crossings, but longer crossings would just have a signal and lines painted on the path. You can see crossing examples by searching for canobie express in google image search.
Also the ability to have switch tracks so you can have a single track around a certain area of your park with a loop at each end and not have to have two tracks side by side or one continuous loop.
Also switch tracks to storage sheds so you don't have to run multi trains all of the time. Just have one train switch out during the day when ridership is low. This could also be great for roller coasters as well. This should also improve maintenance and downtime.