With the maintenance now over, the latest Splatoon demo has pulled an ARMS Global Testpunch, and has an all new update available now.
While the update itself doesn’t realty do much of anything, it has added construction going on in the background of Inkopolis Plaza, as if the Inkling world is gearing up for the Slatfest that kicks off on the 15th of July. It could also mean on the day the event gets underway, a second update could be available that properly transforms the location, or this will happen automatically when you boot up the demo on the day.
But the update is small in size, so downloading it will only take up a couple of minutes of your day, if not less, depending on the speed of your internet connection.
Source: Nintendo Everything