I don't understand why a horse that breaks would have to drop out? It is the same as current racing but they just have to follow the inner outer course.
All horses can still start together with a mobile start - If one breaks there is nothing different. If it breaks anywhere on the course it's still no different.
I think this racing has the ability to reduce carnage because you are putting smaller groups of horses together. At the moment one horse breaks and it can take half of a field out of play.
Figure 8 won't happen because you need to build a track as you said. You wouldn't need to do much at all to implement this idea.
It is something different and the sport needs something different because the same old seems to be leading to a slow death.