Imagine trying to have 200 kids 1.5m away from each other outside; it's impossible. Vaccinations take 2 weeks after the second jab to come into effect and 'rapid antigen testing' talks 1 hour for 10 tests. A lot of parents and students are just concerned with the health risks and I completely understand; health comes first.
"Vaccinations take 2 weeks after the second jab to come into effect"... This is simply not true. Effectiveness of vaccinations does build over time and a second vaccination is beneficial, but substantial benefit has occurred within one to two weeks of the FIRST vaccination. This is why they want to start vaccinating year 12s next week, so they do have significant cover (though not full benefit) by August 16.
On the rapid antigen testing idea, there is a substantial practical problem that the testing needs to be administered by medically trained individuals, which will be a major difficulty if used on large numbers.
As for what will happen next, we can all speculate but no one knows. My opinion, for whatever that is worth, is that the HSC exams will take place in person and under supervision like in previous years, though maybe at different venues and with more distancing, mandatory masks, etc. What schools do about trials - virtual, in person, replaced with other assessments - will vary between schools. As for the lockdown ending by the end of August, I think it is very very unlikely - I'm expecting at least another month to be added.