A couple of features that appeared in Pokemon Sun and Moon have been confirmed to be returning to Pokemon Ultra Sun and Ultra Moon.
According to the product description of the official Japanese Pokemon Ultra Sun and Ultra Moon strategy guide, the Festival Plaza, Battle Royal, Battle Tree, Poké Finder and Poké Pelago will be returning to Ultra Sun and Ultra Moon.
The strategy guide will come with a serial code granting the player 2 Master Balls. It ships on December 6, 2017. Pre-order the strategy guide here (eligible for international shipping).