Those are some really interesting ideas.
I like the "Trampoline" and "Oscillating platforms" ideas. They would be fun and funny to add to tracks.
A few times I've suggested something similar to Oscillating platforms. (Items that can be set to follow a Vector Path) The items could have animated parts (like the wheels on trains) or just be single image objects. Then, when placing the object in a map you click a button "Create Item Path" and are presented with something similar to the Custom Camera in the Mediatracker, where you can position the object at a "Keyframe" then move it on a timeline to another (maybe interpolated) Keyframe and so on until you have your path laid out, then choose a path type to follow;
Once: (object follows the path to the end then stops)
Ping Pong: (object follows the path to the end then reverses and follow it back to beginning)
Loop: (object follows the path to the end then jumps to the beginning keyframe and starts over) Looped should have an option to snap the last keyframe to the first keyframe for seamless loops.
Setting up a path, as I said, could work the same way as we set up custom cameras now with the exception that instead of moving the camera positions around you actually click on and drag the object to where you'd like it (so you see how it looks on the map) and adjust the X-Y-Z-Roll-Yaw positions at each keyframe.
So, you could set up your "Oscillating platform" using this method and make a sliding platform, an elevator, a ferry boat or with looped paths even a pod of Orcas surfacing and diving through the water. Maybe a biplane flying through the canyons, a UFO landing, a convoy of trucks crossing a road or just a confused Duck swimming in a circle.
I think Item Paths could be a really fun tool to add to MP.
Since this idea isn't really a block I think I am going to start a new topic for things like this:
What new feature would you like to see?