I think you are correct. There is going to be a huge churn of players at every level.
The top D3 non high academic teams (Wisconsin Whitewater for instance) might resemble more of a top D2 team, with more D1 drop downs and JUCO transfers than ever.
A big factor will be the 2021 Draft and how many top high school players will turn pro as opposed to joining already bloated SEC & ACC rosters. Further complicating matters is the uncertainty of a new CBA looming in MLB.