Look at the last part of the quote by S.Francis. I quoted that because 36.0 for a 100m Hurlder is very fast, for example WR holder Donkova never ran faster than 38sec, was she able to do it faster isn’t the question here, the main thing is she didn’t need to run faster.
Now they are running 400m, that’s not 300m it’s obvious, but i see it as an extreme choice of overdistance for S. Francis.
36.0 doesn’t adequate to 53.84 but they have no 400m specific endurance which allow to finish decently the last 100m of 400m. Taking in account that Forster is able to run 11.10 at 100m, under 23sec at 200m (her 200m PB is over 23 but it was done in the nineteens), close to 36sec at 300m, the speed curve decay leads to a not so exceptional 400m. Not many 400m runners doing 36sec at 300m can run 11.10 at 100m.
Herb, if it isn’t the case which is why you asked, then i didn’t understood your question. S.Francis was talking about his speed endurance training strategy, and says he starts with GENERAL speed endurance, which refers for him to 300m races, and apparently to 400m races in a extreme point. Note that it isn’t new for them as in 2002, Brigitte Foster did a 55.71 400m the same season she did 12.49. In any case, 53.84 SEEMS a major improvement compared to 55.71, conditions may defer of course, especially for non-specialist.
Simspon is also coached by S.Francis, though i heard that there was some split at some point last year, so don’t know exactly how is their relationship now.
Concerning Burrell in 1991, he told journalists that he took rest after Zürich and did tests 400m in 46.6 and 300m in 33.2. It was some days before Tokyo, so everyone here are similar infor from different sources! 
Pat Connolly used 400m and even 800m competitions with Ashford and with Allyson Felix last year as purification races, so the aim for her is quite different.
The explanation given by Kitkat is very interesting. I know some coaches who start with 400m because “Marion Jones did it”, not knowing why. Flo-Jo started her 1988 season with several 400m, which were horrible, she once opened with 22.9 and finished agonizing in mid53, beaten on the tape by an obscure Nigerian. 5 mounth later she anchored a 48.1 for US team in Seoul…