Sunfish you missed point b2); what if student drops map on floor and enters inadvertent turn into imc, then jams rudder with his Swiss cheese lunch and enters the drop area.
You mentioned all the things that happen to reduce the risk of a mid air canopy aircraft collision. What is the chance of something slipping past;
1) jump plane - student radio contact. Jump pilot broadcasts twice to all freq jumpers pass through
2) melbourne atc traffic warnings
3) ground control on dropzone not seeing aircraft overhead and giving clearance
4) jump pilot not seeing aircraft
5) student pilot not seeing aircraft / canopies then no avoidance action
6) skydivers not seeing aircraft then no avoidance action
7) canopy and student in aircraft on collision course
The danger area is clearly marked on maps, students should be trained on what to do, jump pilots and atc would naturally be cautious of students transiting the area.
Once you work the chance of all that happening you can do a cost benefit analysis.
As with all activities there is only one real way to reduce all risks to zero.
But I guess you don't care about the part of GA which are all "thrill seekers and people having too much fun. There can't possibly be sensible people making a living or benefit from that. Plenty of jobs for the students that can't navigate around a danger zone in aviation going around these days".