Flying from JFK, EWR and BOS to London in business class for 45K miles is one of the best Sweetspots of the revamped Alaska Mileage Program (https://awardcracker.com/new-alaska-mileage-plan-sweetspots/). While this route also works with British Airways, you will end up paying hefty taxes (see the image below).
There are plenty of AA business class seats available for the summer of 2024 through the fall of 2025 (see Seats.aero search results below).
Can we book a one way stopover using AA mixed with another Oneworld airline?
It would have been nice if Alaska’s online multi-city booking allows mixing AA with British Airways so you can first travel to London paying very little tax. Whenever I attempted the one-way stopover booking, the online Alaska booking defaulted to a British Airways flight from the US to LHR segment with very high taxes (see image below).
Conclusion
Flying from JFK to London for 45K miles and $19 in taxes is a wonderful Alaska Mileage Plan redemption. I am assuming that mixing AA flights with other Oneworld flights in the stopover itinerary can be accomplished by calling Alaska customer service.