Relying on quadrantals for protection is the same as trusting the 'big sky theory'
I must be missing something obvious here, but surely the quad/semi rules do nothing at all apart from reducing the speed at which traffic on a recip or roughly-recip track is likely to meet each other.
The collision speed would still be high enough to destroy both planes, in most cases.
Is there another reason for this system?
In IMC it might help with procedural separation but that requires radar assistance to start with, or control of departure times and speed.