Not sure the fares will even be loaded this far in advance for those dates? So it's hard to play around with real costings. You might be best with a 'round the world' ticket if your dates are more or less fixed - the OneWorld RTW planner will give you a good spread of all the flight options available, although the downside is it can be hard to see at each step how the specific choice of flights really affects the total price. For what it's worth, I tried loading that same itinerary for those same dates in 2019 (so at shorter notice than you will book, albeit without any 'Olympic premium') and it gave a grand total fare in business class of just over GBP 6k. That was using the best (Japan Airlines) and most direct flight options at every step...you might be able to try different alternatives and see what comes up lowest, once fare buckets are open. I used London as the starting point for this experiment - I don't know whether the 'ex-EU' trick would make a difference on a RTW fare basis
Someone will probably be along shortly with a cheaper alternative
https://www.oneworld.com/world-travel