@evan Too early to tell. I looked back at 2020, and the field wasn't as big as I thought.
I'm sure a couple of the 2020 hopefuls will be back (Buttigieg for sure, maybe Harris, unlikely Klobuchar and Warren) ... and Harris has never won a primary or caucus, so I don't expect her to be a factor.
Other than that, it'll be "new" people -- lots of governors and senators, maybe AOC .. should be a very interesting time.