IF teams are actually headed to Malaysia (or at least to Kuala Lumpur International [KUL]), they could really be heading anywhere in Malaysia.
There's plenty of flights to Kota Kinabalu, as well as many other locations.
But I would like to propose another option: Bandar Seri Begawan, Brunei
Depending on team departures from leg 1 pit-start, I find it tough to believe that some/any teams could make the 10:20a or 11:20a flight to KUL from NRT, meaning teams were more likely on the 5:20p flight, meaning they would take the next available flight in the morning, leaving at 6:35a
Production could make it there the night before, leaving KUL at 9:35p- plenty of time for them to set up.
Production would have more than enough time for this connection if THEY were able to catch the 10:20a/11:20a flights from Narita.
It's still WAY more likely it's somewhere in Malaysia, but it'd be a cool surprise if they could sneak Brunei in there.