Thanks for your reply, Elisa! A business partner and I are indeed working on this kind of service. I am a professional travel planner and would be able to offer group services beyond offering a guidebook. We could make restaurant reservations, secure private chefs, hire cars and drivers, and really anything else a group would need. Think of it like a concierge service!
Hosts would offer it for free to their guests, we would handle all logistics as a third party (licensed travel advisors), and in return, we would pay the host either a flat fee per person or something along those lines.
Of course, our goal would be to provide excellent service to every single person, but in the off-chance that a negative experience were to come up, our terms would include a statement saying that they cannot leave the host a bad review for our work.
This means there is no additional work on the host beyond recommending our services, and could potentially make a nice additional income on their group bookings. We would most likely be targeting homes with 3 rooms or more.