I believe Wally Mk2 is right on the nail. With police and search authorities now in possession of information from credible eyewitnesses on Bella Creek Rd - who sighted the Dragon circling low over a valley just N of Lake Borumba, then ascending into heavy cloud, just before the reported disappearance time - the scenario is screaming to me, of a CFIT into steeply rising terrain on a ridge surrounding that valley.
No doubt the police and search team leaders have taken this scenario on board, and have adjusted search tactics accordingly.
I'll hazard a guess at this scenario. Des realised he was flying into dangerous IMC and needed to put down quickly. He sighted the cleared valley floor through a break in the murk, and descended to check it out for landing potential. A couple of circles showed nothing suitable for a forced landing.
So, in increasing cloud and perhaps even a rapidly-lowering ceiling, he set off the EPIRB, and aimed at what he thought was the valley outlet, whilst firewalling the throttles for maximum RoC, knowing full well he needed height, and lots of it.
However, flying blind, he picked the direction of one of the sizeable ridgelines that surround the valley, and the leisurely RoC of the Dragon was inadequate to clear the valley ridgeline, and he impacted the ridgeline in steeply rising, heavily wooded terrain, that has a thick canopy.
The impact would have been at a upward angle, roughly equivalent to the angle of the maximum RoC - and the Dragon tore through the canopy, and largely disintegrated upon impact with very large hardwoods at high speed.
There would be little major structural sections left, perhaps only a major section of the fuselage.
The impact point would not be visible from above, it will only be visible to observers flying along the face of the ridgeline, and looking out horizontally at the steep terrain.
This would be the reason why the search so far has found nothing. Observers would perhaps have been imagining an impact downwards from a falling aircraft that they think has run out of fuel - when the impact has been upwards at full throttle.
The impact would have possibly destroyed the EPIRB, thus the short period between activation and the cessation of the signal.