I think this has never really been brought on the table. It's a very interesting question.
Endymion said:
What is likely to happen? With *William IX still a minor at age eleven, who will assume the regency?
I think Eleanor would have great chances of being named regent for her 11 year old brother. There are two reason for me to think this: one is that she is wedded to Louis VII, who is the King of France and regarded as the overlord of the French Nobles (being King). The second fact is the friendship between William X of Aquitaine and Louis VI of France (father of Louis VII): that's one of the main reasons Eleanor wedded Louis VII OTL. I can thus see William X leaving the regency of his son *William XI to his daughter Eleanor and stepson Louis VII of France. The regency wouldn't last long anyway: most of the Middle Age's princely families considered that you were old enough to rule around 14/15. So *William XI would probably have a 3-4 year regency before he takes power.
Endymion said:
Perhaps one of Obviously an independent Aquitaine in the twelfth and thirteenth centuries--assuming *William XI has heirs and the House of Poitiers retains the duchy and its territories--is going to have major effects and butterflies galore.
It will have concrete buterfflies for sure: for one, Eleanor never becomes Duchess and thus is a far less appealing princess. If she still "divorces" Louis VII like OTL, she will be far less attractive princess because she won't bring anything with her, except maybe a few acre of lands as dowry.
Indirectly, it aslo weakens OTL Henry II of England. Even if he does wed Eleanor in this scenario, he won't have the magnificient ressources of Aquitaine: at best, he will have support from *William XI but that's no guarantee. Thus, he will only have the titles of Duke of Normandy & Count of Anjou, Maine & Tourraine. He can still conquer England of course, but it will be harder for him.
And of course, the character of *William XI himself will be important: since he died at age 4 OTL, you can practically have him do anything. He is the wildest card in that scenario.
Endymion said:
Perhaps Aquitaine will regain Toulouse in the near future? The (rather appealing) idea of *William XI potentially wedding Petronilla of Aragon and laying the foundations for an Occitan kingdom comes to mind (assuming of course that she is still born in 1136, and, assuming that the immediate butterflies in the first few years following 1130 are not great, I don't see why not).
I'm not sure the Dukes of Aquitaine would be successful in claiming Toulouse for themselves. The heirs of Raymond IV did a pretty good job at keeping the County of Toulouse for years and were regarded as the legitimate rulers of Toulouse. They even have a pretty strong claim to back their legitimacy. Of course, if there is still an Albegisian Crusade like OTL against the Cathars, it's possible the Duke of Aquitaine takes part in it and tries to reclaim Toulouse: but even then, that is not so sure because the House of Rouergue (I think that's the name of Raymond IV's family) held a lot of influence in that part of the Languedoc.
The Dukes of Aquitaine establishing an Occitan Kingdom is also a bit problematic to me: remember that they were vassals of the French King and claiming a crown would put them at war with him. So, the French King will probably try everything he can to avoid Aquitaine becoming a rival Kingdom. It's also likely the vassals neighboring Aquitaine would side with the French King against the Duke in this scenario, because they wouldn't want a very powerful neighbor. Doesn't mean the Duke of Aquitaine couldn't try, but that will certainly play in the balance when he comes to taking that decision.
Endymion said:
I also can see Eleanor of Aquitaine still wedding Louis VII, and perhaps she'll manage to bear him a son and the union will be slightly more successful, dynastically speaking, than OTL.
I don't know if Eleanor would really be able to give a son to Louis VII nor to stay married to him: the characters of husband and wife were too different. Eleanor came from a rich southern fief, was very cultivated and refined and she felt quite out of place at the French court. For his part, Louis VII was very pious because he originally had been planned to enter the Church: Eleanor often said that she had married not a King but a monk.
On the other hand, Eleanor will need to strenghten her position in the French court because she can't count on inheriting Aquitaine unless her younger brother dies. I do not see her murdering her brother, so the only option would be to stay close to her husband the King of France: for that, she needs to avoid any suspicions of having committed adultery and to stay close to Louis VII. And since giving birth to a son would probably do wonders in that regards, it's likely that she would probably try to get pregnant more than she did OTL (Eleanor and Louis VII only had two daughters, born in 1145 and 1150).
This brings me a side question: what would be Eleanor's dowry if she doesn't inherit Aquitaine? A small Aquitan or Poitevin fief I believe, but which one?