C fare for PHL-ICN allows unlimited stopovers.
Regarding F seats on domestic flights to/from internationl segments, there is no such a rule.
Fare rules are pretty solid and they don't give exceptions to certain fare for stopover rules.
So flying domestic F doesn't make sense.
You might have to pay additional fare because of MPM.
To be honest, I'm not familiar with business fare and first fare, so I can't guarantee about what I'm saying.
According to the fare rule, PHL-ICN MPM is 8328 miles.
However, ICN-HNL-PHL goes up to 9496 miles.
Since there is no non-stop service between ICN/HNL and HNL/PHL, the shortest way would be ICN-NRT-HNL-ORD-PHL, which is 9523 miles.
I'm not sure whether it is MPM fare or routing fare.
If it's a routing fare, you won't have to pay extra fee as long as your routing matches with the applicable routing.
In this situation, you can't go via HNL if the applicable routing doesn't have HNL on it.
If it's a MPM fare, you will have to pay extra fee, and you can have any routing as you want.
In this situation, you'll exceed at least 1200 miles from the permitted miles, so you'll have to pay additional fee.
If your trip is a few months ahead of now, I can visit United CTO in the next month and inquire about it.
Have a fun.
I'm visiting HNL next month as a transfer without stopover.
I think there are some F/C guys who can help you about this.
BTW, I'm a V/W/S/T guy, never flown anything higher than V yet.
Damn, V class on 24MAR for HNL-NRT is available.
