If we get a different meet & greet character at SNW, Donkey Kong, Bowser Jr., or Daisy feel the most likely, as they already have costumes that have been used at the other parks.
I mentioned this previously, but I think there's a very real possibility we see Stranger Things at the event next year. It would line up with the final season, and doesn't lean so far into horror that it wouldn't work at an event like this. It also attracted a lot of cosplayers when it was featured at HHN, which Fan Fast seems to heavily encourage.