The runway is "only" 1000 metres long.
They have it parked somewhere near Tokyo.
It is just a test.
In the future they may plan to use the technology for civil aviation, but my guess is the first application will be to alleviate Okinawa's burden of hosting the US military. There has been talk for several years now about moving a helicopter base offshore in Okinawa.
By the way, Kobe (very near Osaka) will start building an offshore runway on a manmade island very soon. Nagoya (an hour away by train) is building a similar project. Osaka has started pouring dirt to build a second island right next to Kansai Airport (KIX) to add a second runway.
These projects make floating, mobile runways a serious possibility (especially if sea levels rise 5 meters in the next 100 years!)