I wouldn't count Anne de Bretagne out so soon. Queen Mothers had a special place in French tradition and tended to have strong claims to the regency.
Indeed, but they as well tend to not have holdings on their own, critically as strategical as Brittany. Neither Valois, Valois-Orléans and their clientele are going to be much comfortable with a "landed" regency (too many bad souvenirs from when it happened earlier).
Giving *Charles XI would be really young and, let's face it, still likely to die before being sacred, Louis d'Orléans (as his immediate heir) would likely have major support from Valois and their court.
You'd argue that Louis was as well landed, but Orléans was really less autonomous than Brittany at this point, and mostly was about fiscal revenues than political/strategical importance.
However, I think your forgetting a key player: Anne, Duchesse de Bourbon.
...She's the
second person I mentioned in the post you just quoted, right after Louis d'Orléans...
She would have a strong claim as well. Chances are we'd see some sort of triumvirate between the Queen Mother, Anne and the Duc d'Orléans.
I think that (and as you said) Anne de Bretagne possibility of being regent would make her more likely to support Louis d'Orléans this time : would it be only because he was far more close to Valois' interests, was still likely to inherit and by sheer defiance against Anne de Bretagne (as she proven IOTL).
As for remarriage, I doubt it.
Remember Queens of France didn't remarry, not if they didn't have to.
Anne de Kiev, that married Raoul de Vexin, without any kind of pressure, would like to say a word about this.
Or Mary Stuart, for that matter.
(And of course Anne de Bretagne, that wasn't exactly forced ton managing to get a better deal with Louis)
This "rule" is painfully absent from any I could went into, except non-contemporary statement often attributed to Blanche de Navarre (but only only, as every scenic history, persons concerned often vary) "Queens of France doesn't remarry" that isn't a statement about a rule, but about her own opinion.
Queen of France didn't easily remarried because they often outlived their husbands while being out of mariage date (or because they found that marrying would have made their regency/influence on regence harder).
Would it be only, as said above, to keep Brittany close to Valois interests, and maybe promising her part of the power in the Regency, a remarriage seems quite possible.
Here Anne wouldn't need to remarry as she already has an heir in her son Charles IX.
You mean a really young son, that is still likely to die in infancy? Honestly, I saw better odds than that, for a stable succession.
Not to mention that it could weaken Charles's claims to Brittany if he has half brothers.
Possibly, but nothing said that Charles HAD to get Brittany no matter what. Giving away a title for a younger Valois isn't exactly unheard of.
The main opposition would be rather, and it's a really valid one, that half-brothers of Charles IX being too close of the throne (which is why I don't think it's bound to happen)
But there, I doubt Anne would be really allowed to have any real influence on the regence, at least de facto : no remarriage would make her being seen suspiciously at best.
As to Italy, I doubt there would be any further attempt during the regency. Its very rare to see foreign wars during a King's minority.
It's rare, but again, not unheard of as during the minority of Charles VI.
Giving that Louis is still likely to inherit at this point, and that in order to enforce Valois' claims on Naples you'd need strong points in Italy (likely maintain of alliance with Borgia) and that the need to strike within historical "window of opportunity" would be obvious for everyone...
That said, I'd see a more cautious Second War of Italy, there.
On the other hand, I wonder if we could see an Orléans expedition against Milan, funded and led by Louis instead of by the Kingdom of France. It would be similar to the d'Anjou invasion of Sicily in the 1200s.
That's unlikely to happen with Louis d'Orléans being regent or at the very least being part of the Regence. Charles d'Anjou had the "benefit" to not being considered regent-material.
Finally, its impossible to know what Charles IX would do once he comes of age. I can see his mother and aunt being against further Italian expeditions and discouraging them in their young Sovereign.
I don't exactly see why, there. Nobody really prevented Charles VIII going to Naples and the whole political/background in the court was all about Italy.
It's really unlikely that Valois would just "gave up" on Italian opportunities : a series of defeat and half-victories didn't made that IOTL, after all.
You know I'm not a big fan of "After a PoD, random **** happens". Eventually there's such a thing as historical tendencies and political background.
Flanders were gave up at least since Louis IX's reign, as too costly to conquer and even more so to maintain.
The Italian policy of Valois comes from more than Charles VIII suddenly deciding "I'm going to Italy, because." but from Italy being a political beacon for reinforcing Valois presence in HRE (in places where, at the contrary of Flanders, you could actually get allies), reinforcing prestige of Valois and eventually (it shouldn't be overlooked) abiding to a late Crusade spirit (that can be found in Late Medieval chevalresque culture, that appeared first in Burgundy, and then in French court) where southern Italy could be used as a base to counter Ottomans.
There's really few chances for the latter to happen, of course, but that was part of the motivation of not only Charles VIII, but from the French nobility in general.