This is not specific to the vivoactive 4, but a general suggestion for Garmin's health/lifestyle watches.
Personal activity intelligence (PAI) score is an independent measurement of fitness which has been developed by Norwegian researches. It has proved to be a better indicator of overall health that traditional measurements of physical activity, e.g. individuals with high PAI do not suffer increased mortality risk from prolonged sedentary behavior (more details and links to studies can be found here https://www.paihealth.com/science-of-pai/default.htm).
PAI score would be a great addition to Garmin's health/lifestyle watches and it would help us toward better everyday health. Apple and Fitbit already support PAI and it would be beneficial for Garmin to also support PAI and contribute to standardizing the metrics we use to quantify health outcomes and ensure access to this important health indicator for Garmin's wide user base.