An SBS suggested that Ryokugyu, like Fujitora, has an anti-World Gov agenda.
I expect him to show up and do something impressive that hints at his power. I think the cleansing Wano theory is a good one- like Aokiji freezing the seas or Fuji lifting the rubble, it shows power without an actual fight.
But I think his role will be a more interesting one than showing up and fighting.