This 'cognitive impairment' would appear to be a massive can of worms not just for display flying, but for any type of flying. As AvMed courses have long drilled into us, the human body is not designed for the things we do to it in the air. Displays are an extreme example, but even routine operations are full of potential for illusion, error and misjudgement. I had an instructor who reckoned that the successful pilot was someone who left the smallest proportion of their mental faculties on the runway.
If 'impairment' of the sort that leads to flying below minima and missing gate heights is considered grounds for acquittal from criminal charges, it rather undermines the idea that a pilot could be held to account for their actions. Some degree of 'impairment' can always be argued.
Besides, isn't being aware of the potential for impairment, and taking appropriate steps to mitigate, an essential part of piloting? Just the act of beginning that display was arguably reckless given the currency and experience issues.