Currently, Navigation has two modes – allow HOV access (for example in CA with allowed stickers), or no HOV lane access.
Occupant detection could be the third choice. In this case, it would know the requirements of the HOA lane (2+ or 3+ occupants) and check if that many are in the car. When it detects that number of occupants or more, it will include the HOA lane in available lanes when navigating.
(lightly edited by moderator)