For example, your HVAC, water heater, central circuitboard, and central air system can have maintenance schedules and technical info, but that can be hard to know, because all you usually have is a model number.
Likewise with the coming home solar revolution and home storage systems, there will be other major systems that will be long lasting and major cornerstones of your house.
Also, your utlities can provide info. All of it can be centralized into a dashboard.
What I want to avoid though is the geewhiz smarthome. Sure it can integrate with that eventually, but I think people would like better info about a basic dumb home.
Maybe provide a service where someone comes (or they send you a kit) to scan the house with those things that can see through drywall, scan for heat maps/leaks, or just scan the shape of each room and form a map of the house. Of course this provides opportunities for upsales and the like.