It would be a cool twist if it will be the next island the SHs will go next. Imu's weapon could be the classic "time bomb to stop" every arc,or,but this second option is probably too dark for One Piece,imagine this: the SHs save the country,they say hello and leave,and suddendly,you see a glimpse of Imu's weapon like in Lulucia,and the island gets destroyed! Dark but cool.