Yes - certainly DE systems present that versatility as far as power plants are concerned in that the alternators can be turned by anything, as can hydraulic pumps for that matter!
I do believe that the world is steadily moving away from nuclear as a source, because of the 'dirty' connotations that come with it, but that would not preclude mega-yachts from being powered by a mini-reactor.
So what would the world be like with a hundred mini-reactors cruising around the oceans, running aground and having collisions with each other! The Greens will go bananas!
Interesting, none the less.
And sure - solar is hardly worth the mention as a source.
What interests me more will be the construction material and methods of the mega-yachts of the future.
Wooden sailing ships will have their day again, surely?