My opinion only but I believe this is going to go down like a lead balloon in the HCA and the applicant is going to receive a severe dressing down by the Bench.
We have 2 cornerstones of modern criminal law at play here, the burden of proof resting with the Crown and the right of the accused to silence (or to say as little or as much as they want). The fact that an alternative theory that was relied upon during the appeal wasn't advanced at trial is totally immaterial, it is incumbent on the jury to consider any and all possibilities which may be consistent with innocence of the accused. Straight from the Bench Book -
If there is any reasonable possibility consistent with innocence, it is your duty
to find the defendant not guilty. This follows from the requirement that guilt
must be established beyond reasonable doubt.
Note that it doesn't say 'you must only consider the alternative scenarios advanced during this trial', if this was the case, the many cases where the defendant relies totally on the Crown proving their case as opposed to giving evidence themselves, would inevitably result in conviction as no alternate theory exists. Very simplistic I know but imagine the following - A murder case is prosecuted entirely on the basis of 1 witness who saw the defendant in the vicinity of the crime and no other people were present, no other evidence exists whatsoever. Confident of acquittal, and rightly so, the defence does not call any witnesses or cross examine any prosecution witnesses. The only theory proposed to the jury is that the defendant was the only person observed in the vicinity and therefore must be the killer. If what the ODPP is proposing held true, the jury would be prohibited from speculating on ANY other reasonable theory (the accused was on his nightly run or was going to the service station to buy a bottle of milk etc) and conviction would be the ultimate result despite there being any number of reasonable hypotheses consistent with the innocence of the accused. As I've said before, we must all remember that the burden rests with the Crown to prove guilt and the jury must consider ALL reasonable possibilities, including those not advanced at trial, during deliberations.
You might be critical of the tactics used by the defence but we must remember that they were defending a charge of murder, had the ODPP elected to proceed with only a manslaughter charge you would have seen the trial run a very different course indeed.
As for the appeal outlining (in part) financial pressures playing a part in Allison's death, this is a very long bow simply because Allison's life insurance was emphatically disavowed by the prosecution as a motive for murder during the trial. With there being no financial benefit outside of this policy (indeed, Allison's death would almost certainly have had an adverse affect on Gerard's finances), it genuinely boggles my mind why the submission to the HCA makes any mention of it whatsoever.
As for post offence conduct being intractably neutral (as per the QCA), there are any number of authorities that can be relied upon (some of which I have previously linked) where an unnatural death has occurred and the perpetrator has gone to great lengths to conceal their involvement despite the death being totally accidental. The community might consider this behaviour morally abhorrent but it's far more common than you might imagine. Again, I cannot possibly see how the Crown could possibly argue otherwise.
In my opinion, if a private citizen (as opposed to the Crown) were to persist with applications or appeals of such limited merit, they would run the very real risk of finding themselves declared a vexatious litigant. While obviously I feel for Allison's family, friends and Allison herself, at face value this looks to be a politically motivated application and one that would NEVER have occurred had the case not been one with such a high profile. I do feel for Byrne QC, he was between a rock and a hard place and while I don't know if the QLD Government placed any pressure on him to pursue the matter further, there must have been tremendous pressure on a personal level knowing that the majority of the state, if not the country, were outraged at the downgrading of the charge (despite it being legally sound in the opinion of literally every qualified person I've spoken to). Do you accept the decision of the QCA or do you proceed with the flimsiest of cases, knowing full well that you have Buckley's of being successful (and chewing through literally millions of dollars in taxpayer funds in the process) but with the blessing of the majority of the community? It would have been a tremendously difficult decision and I don't envy him whatsoever.
And just quickly, I know many on here were outraged that a jury verdict could be overturned but let me leave you with the following recent case in the NT to consider -
http://www.abc.net.au/news/2016-03-24/murder-verdict-overturned-in-darren-ashley-case/7275092
3 jurors, that's one quarter of the jury, totally misunderstood or even worse, blatantly ignored fundamental legal principles that were drilled into them numerous times during the trial. I will concede that juries usually get it right, but they are FAR from infallible. Just 1 person, nevermind 3, has the potential to taint the entire process and see someone spend the rest of their life in prison when they should have been acquitted. How many times does something like this occur when it is not brought to the attention of the court? I genuinely shudder at the thought.