I think that was tried before.
Rivers, as far as I know, don't change anything for most units - except to raise the move cost.
Landlocked cities I came accross a solution for. Add airlift to the ship. Thought I don't see why you want a ship inland.
The only way for workers to modify terrain is the Plant Forest - unless there's something in C3C that I don't know about, since i don't have C3C still. I don't care to start fiddling with the code for that yet.
Finally, the closest I think you'll get is to make it an moving air unit. I will look into alternatives, but I have quite a bit of work to do, so it might take some time.