I would greatly enjoy being able to add an engine to one of the excellent ship blueprints, then decorate, load it with cargo and live on it. I have extensive waterways in the java version, as I like water, and will likely want to add even more in the new version. Ship wise, the game "Salt" accomplishes some of this. Even more importantly, most mass goods are shipped over water when possible for obvious reasons.
This may be a candidate for plugin... I did find the "SimpleCars" plugin that, with modification, may serve as the basis for a mobile ship. The ship would need to have the ability to have things attached to it, unlike the current boats which have no cargo capacity. As a workaround, I would be thrilled if I could simply slap saddlebags on the boats.