I wouldn't be so sure. I think most agree that G. Dibaba's center event is 1500. She's gone up to 5K and done extremely well, her outdoor is top five all-time, if I'm not mistaken?
So going down to 800 would seem more natural.
Using the Van Niekirk comparison, if his center event is 400, like 1500 is to her, then 100 would be two events down, just like 400 is two events down for her. 800 would be one up to him, which he has never tried to my knowledge. With each event up the aerobic becomes more prevalent. He has already gone sub 10, but not nearly among the contenders in that event.
If she had a similar result in the 400 it might put her at 50/51. But again, sprint training is much much different than even mile training.
We'll have to see what she does next week. She will likely be pulled by Semenya, which will also be interesting because Semenya is a back of pack runner, which would seem to be what Genzebe would be forced to do being that she's coming down in event. I'm also curious if she will feel out of her element against these giant women(?). She's never run a race against big girls before, she does, however, train almost exclusively with men.