Hi,
I didn't read the whole thread, but here's my personnal experience.
I flew to the Philippines in January 2017 with a P4, travelling with Emirates.
Concerning drones transportation, the aerial company specifies that drones cannot be carried as a hand luggage, and that batteries (drone relative or not) cannot be put in a checked luggage. Kinda annoying.
Anyway, I managed to transport it from France up to my final destination (Lille-Paris(Train)-Dubai(Air)-Manilla(Air)-Naga(Taxi+Bus)).
I had to carry the batteries in my hand luggages, in fire retardant bags, and the drone was carefully packed in my checked luggage (among towels, socks and all

).
Wasn't very confident, but I had no really other choice since I was already travelling with a quite big amount of things to transport (off for a wakeboarding trip).
I read that I could easily dismantle the legs of the P4, but I have not done so, since I found the legs to bring additional protection to the gimbal.
In the beginning, I wanted to buy a Mavic, which is, say, way easier to transport in such journeys, but y'all know the supply problems this little bird had at launching.
I guess that if I'm on for another trip like this, I'll switch to a Mavic (v2 ?) which will be more convenient for my usage.
During my stay, I had no problem flying the drone. But I was always filming in kind of isolated/private areas.
Cheers, hope it helps

Oscar