I've not heard of Ivy '21s reclassifying but here's a vignette that might be interesting. My daughter is a vb player (the athlete in the family!) so we follow that sport as closely as baseball. One of the best setters in SoCal committed to Yale in the '21 class but then announced she would reclassify as a '22 and take a gap year. She's an elite get for Yale so perhaps they accommodated her (she's got very solid academics as well). Just one data point in a different sport but it bears watching for baseball IMO.
If I had to guess it is more the case of kids taking gap years that are already in school. I think a year completely off of baseball is a bad idea (especially as a hitter and compared to other sports) and lots of training can be done during a Covid gap year. Hopefully one has spring/summer opportunities to stay relatively sharp.
I specifically know of several women IVY hockey players that have taken a gap/Covid semester right now and will react with what they year about the remainder of this year. Zero reason to go back if you are gapping as a NESCAC player as they started out the fall as a "we will see about a January start" and now are done for the year. The Ivies are different. The Ivies do have hockey players (men and women) on campus training to some degree at various schools.
Baseball is still a wait and see for 21 and beyond but would be a pretty big gamble imo to take a gap year unless there is specific baseball training involved in the gap. Easier to gap when you have a fall sport (am guessing that there were a decent amount of Football/soccer gaps in Ivies and NESCAC schools).