Just a couple of random thoughts--not the expert here but a big fan--
1) In 2000, there were A and B standards for the marathon when the United States sent just one athlete per gender. The winner of the trials race (s) DeHaven (m) and Clark (w) who both did not have the A standard, but were selected to run in Sydney based on their win. There were others who had achieved the A standard, but did not go. This a mute point though as it sounds like this time around, athletes need to have hit the standard or qualified via the added potential criteria of either a) top ten in Doha , b) top five at a gold label race, or c) top 10 at a world major.
2) I suspect there may be more Americans achieving the marathon standard via the six majors (Tokyo, Boston, Berlin, New York, Chicago and London) or by venturing into Canada to run either Toronto or Ottawa---both gold label races.
3) Question still unanswered---Can an athlete get a marathon standard after the Atlanta trials? The timeframe for qualifying is January 1, 2019 to May 31, 2020? Again, I saw the question --for instance----if a male runner runs 2:13 at the Atlanta trials (and three runners who already have the standard finish after the winner)---can the winner achieve a qualifying time or place in a major or gold label race after Atlanta (up till May 31)?
4} Will a marathon major run this spring and in 2020 (both within the window)---count for both 2019 and 2020 (i.e. Tokyo, Boston and London)?
4) Athletes need to do their homework when looking for that "perfect" race set-up. IAAF certified courses only. No courses such as CIM or 11th place and after finish in Boston. As noted by someone on an earlier post, notable fast, flat and certified course in the U.S. (or for those not willing to venture overseas) should attract a large grouping of athletes trying to achieve an Olympic qualifying standard.
While the Japanese will have a marathon qualifying race in September, their standards to get into that race are tougher than the Olympic marathon standard. As of today there are 16 Japanese women and 17 men with Olympic qualifying times in races held since January 1(basically from just three separate races per gender--all in Japan). Can a race (time trial) such as the one held in Jacksonville in January '16 to secure trials qualifying times be set up? noting that a 2:11:30 or 2:29:30 is going to be a very tough task.
I have read a lot of comments on the board about fairness and the IAAF should have done this or that. It will not change so I think our administrators, coaches and athletes need to plan accordingly (in many different aspects) to make sure the U.S. can send a full complement of marathoners to Tokyo. Sorry if there is any redundancy, but just wanted to add to the discussion.