just a link to the reference.
http://www.urukia.com/utopia-floating-island/
The idea around it is good, solution on how it should float, move, be stable is also quit good, since they have not broken or great something new, they have just used something that exist on the marked, it's called a floating oil platform, that can move by them self, we have one or to of them here in Norway, and they are mainly used for finding oil. the difference between a oil platform and that concept, is that a oil platform is more top heavy, so often the man in charge of loading equipment on them is an engineer... but that's normal!