ex-TYO doesn't have YQ, only YR which isn't very high. You're free to use any carrier you want without huge implications to cost (fluctuations of a few hundred dollars, not thousands like you see on ex-OSL). UK APD is definitely something I chose to avoid, France has the solidarity tax that adds a fair amount, HKG tax is high even for transit, etc.

​​​​BTW since this thread started, DeltaFlyingProf ex-CAI just dropped significantly. There's a lot of discussion of it in the OW Explorer Pricing thread. I just booked a DONE5 for about US$4700, DONE4 is only about $80 cheaper, so might as well add the 5th continent. But it does seem that the OW tool is having issues with itineraries including Oceania (OZ & NZ), some are working, some aren't and are throwing a HUGE base fare difference. (If it's working correctly you'll be seeing a total price in the range of AU$6000-7500). I had no issues though with Africa and South America pricing correctly. That price may not last long, hard to say. *A already updated pricing to reflect the devalued EGP.

Note though everything you book ex-CAI will route to QF for ticketing, which can cause immense amounts of frustrations during future changes. Some people are getting AA to ticket, but you have to call and must have an AA overwater segment. I doubt you could get CX to ticket since the first segment wouldn't be on them and I believe that's their requirement.