I think the McMansions would make great modern-day group homes for seniors who aren't as active as they used to be but aren't ready for assisted living. You could put a full-time caregiver in the "master suite" - free housing - bedroom, sitting area, full bath, great closet - in return for providing transportation, assistance with daily activities, etc. - and then put an individual (or even a couple, depending on the room size) in each of the other bedrooms. With the McMansions' massive kitchens, cavernous "family rooms" in addition to formal living rooms and dining rooms, there's plenty of space for activities, relaxing quietly, preparing meals for a sizeable group, etc.
Some mods might need to be made in bathrooms - low-step showers and high-seat toilets, for example, and a chair lift might be required for some, since two stories seems to be the norm. But imagine the community that could be developed - the relationships, the reduction in anxiety, the increase in social nutrition and actual nutrition from regular meals and someone to eat them with.
I know, I know... zoning blah blah... nursing experience blah blah... reliable help... blah. It's a dream!