My toxic trait is that I am far more interested in the socio-economic and geopolitical implications of ABO settings than the smut.
For example: I can't read any ABO AUs set in England or France because while I can suspend my disbelief far enough for a gender trinary set up, I can't suspend it enough to believe those two countries would still be distinct entities in a alternate history where Richard the Lionheart could have impregnated Philip II.
If there was a viable dynastic future with Richard, Philip would have climbed him like an oak and dragged him to the altar if he had to. It's a match that makes perfect sense from both their points of view: Philip gets Aquitaine back under French rule, the best general in Europe on his council, and a powerful check on the Angevins... then unexpectedly (after Henry the Young bites it) the entire Kingdom of England for his Capetian dynasty. Richard meanwhile gets to stick it to his father, secure Aquitaine's prosperity, and gets the leverage to start pushing for his mother's release. Then when Henry kicks the bucket Richard doesn't actually have to be King of England in anything but name: Philip can run the countries and unify the Crowns and what not while Richard runs off to go Crusading.
Plus they also like, loved each other and stuff and being able to get to be together long term instead of being torn apart by politics would have been cool. But I'm mainly obsessed with the historical and dynastic implications.
All this to say any ABO au set in England or France that doesn't have them united as a singular Anglo-Frank empire is doing it wrong.
The concept of A/B/O also introduces the question of what succession law would look like under a gender trinary. England historically used cognatic succession, where female scions and their descendants could inherit titles if there were no surviving males from the previous dynast’s line, whereas France used agnatic succession, where succession could only pass through male lines.
In this AU, it’s unlikely that an Anglo-Frank union could last due to differences in succession laws between the two realms. What would happen if an Alpha died without an heir? Would Betas be treated similarly to Alphas for succession purposes? Could succession pass through Beta or even Omega lines? Succession laws were quite difficult to change, with modifications to royal succession often resulting in civil and/or international wars.
So I see your A/B/O geopolitical hypothetical and raise you that while Philip WOULD climb Richard like an oak and bear him multiple viable heirs, the Anglo-Frankish Union wouldn’t last long due to differences in how the kingdoms would be inherited by the descendants of those multiple heirs. And with the complexities of succession laws in a gender trinary, the War of the Roses would only be more insane.
