Don't remember if this was ever brought up, but I've noticed something when looking at the full Spirit list: events with new Spirits seem to come in at least pairs or trios between DLC characters.
Between launch and PP, we had two: the Let's Go event and the Mario event.
Between Joker and Hero, we got three: Toy-Con, Peachette and Link's Awakening.
After Banjo, we got Tockles (added separately from the main DQ board), Daemon X Machina and Tetris.
Finally, after Terry we had SwSh, Resident Evil and Astral Chain.
The only exception is the time between Byleth and Min Min, but I think it's due to them setting up for season 2.
So basically... after Octopath, we could be seeing one or two more events with new Spirits, if things work like they did during FP1.