Way too early to guess.
As someone already mentioned, field size is a massive variable.
But another is whether the October 2021 race even happens. If it doesn't, they'll continue to let those people attempt to register for the next live one (I assume?). And those people are still working with BQ's from as early as mid/late fall 2018. Plus, more and more of them are getting "better" BQs by getting older -- your BQ is determined by your age on race day, so probably 10-15% of people are getting an extra five minutes added to their BQ margin each year.
If the October 2021 race happens, I'd think April 2022 gets much more normal. Fewer races in the qualifying window than usual, probably less international interest out of Covid fear/uncertainty, probably less repeaters than usual because lots of the October 2021 racers will have been trying to do this race since spring 2020 and will just be burned out / glad to be done with it. If it's a full field, I'd guess no cutoff. Even at a reduced field, I'd guess a much less rigorous cutoff than this year.
Sucks for people trying to race and time for a BQ, but all the more reason to just target the fastest time you think you can achieve, and let the chips fall where they may as to whether it's good enough for Boston.