Was talking with our chat during a stream and it was suggested that Splatoon 3’s hub might be Nagoya, Japan. Along with both having old Japanese buildings, they both have a twisted tower and eiffel tower lookalike.
Not 100% sure of course so take this was a big grain of salt.
*SPLATOON 3 SPOILER* enough time has passed that I think it's worth pointing out if you wait long enough near the rocket you can actually hear human speech coming from the speakers #Splatoon3#NintendoSwitch
(It should go without saying but don’t actually take this any more serious than choosing the direction you put your toilet paper, that’s the point of splatfests)