DL-VA will happen for a while, but all the evidence - even the new livery - suggests that Virgin Australia's destiny is some form of merger with Air New Zealand.
At that point we can expect a CO-UA style re-allocation of fleet resources, and VA-NZ will almost certainly move its 77E fleet to fly from BNE, MEL and SYD to both LAX and SFO. At that point the non-stop AKL-SFO flights would probably be downguaged from a 744 to a 789 and extended to London.
Air NZ would simultaneously close its AKL-HKG-LHR flight and instead operate its two daily 1-stop London flights as a AKL-LAX-LHR 77W and a AKL-SFO-LHR 789, while also increasing its Tasman yields by operating into BNE, MEL and SYD connecting to V Australia / Etihad services through Abu Dhabi to London, Manchester, Frankfurt, Munich, Brussels etc.
The beauty of that is that it restores demand for higher-yield seating on the Tasman flights, and that passengers flying AKL-BNE-AUH-MAN/FRA/MUN/Rome/CDG would arrive quicker than if they took the 1-stop NZ flight and then had to transfer at LHR.
Believe me, a DJ-VA-NZ tie-up is progressing fast. And my own private theory is that that is what DJ management has wanted for the last couple of years, and was effectively using DL as a means of attracting the suitor they really wanted, which was Air NZ.
