Okay, after some more research, I have come to the conclusion that all EFI Hondas can use at least 6000 km/6 month intervals (6th gen), and 7th gen onwards can go 8k km/6 months, with mineral oils and driving in severe conditions, regardless of weather it has O2 sensors. The car should be well maintained and using good quality oil filters. It can be stretched to at least 16k km/1 year if the drive is mainly on highways. I am thinking of trying a 16k km interval on our Civic, and report back with a UOA; it is almost exclusively a highway driven car. The valvetrain was sparkling clean the last time it had its valve lash adjusted, so I'm sure it currently has no sludge.
Fuel dilution, which affects OCI's, is not a problem with EFI cars, even if they don't use O2 sensors. It is a problem with carbureted and GDI cars. However, non O2 cars are still hard on spark plugs.