This would be really confusing, either you have 100..0 which would be a reversed range on it's own. Or you use (0..100).set_by(-1). But using both is just plain confusing, I read it as reversing a reverse range. So when seeing (100..0).step_by(-1) I would expect the same as (0..100).
But maybe i'm overthinking it..
Edit: when I compared (100..0).step_by(-1) and (0..100) I forgot about 100 being inclusive and 0 exclusive in the first and the other way around in the second. But the point I tried to make still stays the same 