Well, I think she is probably already capable of a low 49, and that's 3 seconds faster than anything before this year, so the magnitude of improvement to a 48, then under, is not large in the context of what she's already done.
Leg speed may ultimately limit her top end speed - someone has pointed out, quite rightly, that Marita Koch had superior 200m speed (at least, you'd hope so - imagine Semenya running 22s for 200m as well), but right now, nobody knows where the ceiling exists. If I hadn't seen a 400m run like a 1500m race, I would not believe it.
One thing to remember is that in 2009, pre- first treatment/intervention (which we're not supposed to know about, and around which there's much misinformation), she was an 18-year old, straight out of school, without any advanced training, running 1:55. Add 7 years, same physiological situation, and a 1:52-1:53 is not inconceivable, and nor is it inconceivable for a 1:52 800m runner to have a 48s 400m capacity.
We'll see. I really hope she goes for the 400 and 800, and gets into some really fast races. The clock will have the final answer.