Yes something like this even though Yoshida already said that the PVP will includes vs against his Dev-Team and including Wada as an event.
However, the idea behind this cameo appearance for PVP would be to sorta like climbing the floors in a tower and the further you reach, you can select multiple monster/characters from previous FF series.
So not neccessarily in a sense of climbing the tower but to basically move forward through the branch structures laid out. This would be a great additional ways to earn Achievements and Gils or Weapons/Armors.