I can't speak to the specific merits of that policy approach, but I can provide some legal considerations to think about when it comes to the burden of proof.
To start, in the criminal law, for the most part, it's the Crown that needs to prove all the elements of the offence beyond a reasonable doubt, and any reasonable doubt must result in the acquittal of the accused. That was first recognized in the 1935 House of Lords decision in Woolmington. It's also known as the presumption of innocence, which was incorporated into the Canadian charter in 1992. The jurisprudence on the presumption of innocence has been pretty straightforward in the sense that any time a person may be convicted without a reasonable doubt, courts would likely find there to be a violation of the presumption of innocence that would then need to be justified under section 1 of the charter.
Something you might want to think about is that the reason we have this reversal of the burden with respect to the accused raising the defence of extreme intoxication is that in those cases—as it would be if someone had a mental disorder or non-mental disorder automatism and had, for example, committed an offence while sleepwalking or having a seizure—we're dealing with the internal mental impairment of the accused. The Supreme Court indicated that in those types of cases, it would be very difficult for the Crown to prove internal mental impairment of the brain of the accused, and the Supreme Court justified having the reversal of the burden in those cases to require the accused to prove on a balance of probabilities that they were in that state, so there are special considerations as to when such a reversal of a burden of proof could be justified under section 1 of the charter.
Those are some things you might want to consider.