We did several times during the Dragon Ball manga Knowledge of the oozaruor those forms of giant monkeys (among other things, Oozaru means giant monkey) that occur when the Saiyajins observe the full moon and their tail is intact. The transformation was triggered several times over the course of the saga.
However, these practically disappeared at the end of the Saiyan saga. Dragon Ball Super was never able to bring the monkeys back onto the field with disproportionate force? At the moment, Goku and Vegeta have lost their and we don't know if it will ever grow back. The same goes for Gohan, while Goten and Trunks have never been seen with the famous Saiyan attachment.
Considering that the peak of power for the Saiyans has reached between super and divine transformations, bringing back the oozaru would allow us to explore new avenues: we could imagine one Super Saiyan Goku in this formor reach a new stage of transformation using a process similar to that in Dragon Ball GT. The fourth stage Super Saiyan is unlikely to make his debut in Dragon Ball Super. considering that Ultra Instinct symbolizes the height of power at the moment, but never say never when it comes to the Seven Spheres franchise.