So I did what I consider a very very back of the envelope calculation to try and figure out how many bibs were sold for the Marathon and HM. I went back to May and counted the number of DIS posters who stated they got a bib. There were 49 in both the Marathon and HM (includes Dopey and Goofy). I then went back to the last several years of the Excel sheet I make for the weekend to see how many runners are on it per race.
2020 M - 67, 2020 HM - 59
2018 M - 97, 2018 HM - 78
2017 M - 61, 2017 HM - 59
I then went back and looked at the % the DIS'ers made of the total # of bibs for each race:
2020 M - 0.36%, HM - 0.22%
2018 M - 0.35%, HM - 0.09%
2017 M - 0.25%, HM - 0.21%
So for the M, DIS'ers made up about 0.3% of the field. And for the HM, DIS'ers made up about 0.2% of the field. So if I use those values on 49 DIS'ers from registration day, then I get 16,000 bibs for the Marathon and 24,500 bibs for the Half Marathon.
So either DIS'ers make up a much larger proportion of the total field, or we're looking at 16,000-24,000 bibs for the weekend. On its face though, this estimate seems way too high given the pace at which the weekend sold out at and runDisney stating unofficially there was a "reduced number" of bibs. So I'm leaning towards the DIS'ers are making up a large proportion of the total field than in 2017, 2018, or 2020. But to get down to the 1600-3000 range, DIS'ers would need to make up 2-3% of the total field.