The POD to this is simple, shortly before Louis XI’s death Dauphin Charles passes away of an illness. This leaves Louis XII as Louis XI’s successor. So what happens next? Obviously Louis XII is going to pursue the annulment of his marriage to Jeanne of France sooner and will try and earn Anne of Brittany’s hand in marriage. He would probably push his claim to Milan sooner as well. The Mad War is likely butterflied as well (at least as we know it). Would Anne de Beajeu oppose his ascension? What effects would this have on Europe?
WI: Louis XII succeeds Louis XI?
Maybe, it's not impossible. But the impression I got (which could be incorrect) was that Louis XII only bothered to push his 'claim' to Milan because he needed an excuse to continue the war he inherited from Charles VIII (Charles had claimed the Neapolitan kingdom on the basis of his Anjou grandmother, but Louis of Orleans didn't share that grandmother, and so another excuse was required to continue war in Italy).
But if Louis of Orleans inherits the throne from Louis XI, then he's not inheriting a war. Which means any Milanese ambitions on his part will have to start completely from scratch. That's hardly impossible, but you might see military activity delayed until Louis has firmly established his kingship. IDK, I don't know a lot about Louis XII's personality.
True, though from what I have read it seems that Louis was interested in pressing his claim to Milan before the Italian Wars even started. Though if he didn’t have an interest in it he could always develop an interest and focus on Brittany, Burgundy and England. I doubt Louis would press his “claim” to Naples in this timeline, since his claim was shaky enough in OTL.
On another note Louis’s sister Marie would be unmarried at the time of his ascension, so any ideas who she could marry? I think Maximilian might be possible if Louis wants to reconcile with him and end the Habsburg-Valois rivalry.
True, Richard III is possible if Anne Neville still dies on schedule, though is Anti-French policy may get in the way of that (maybe he goes to war with Louis, but it goes horribly wrong and he decides to marry Marie as part of the peace treaty?).
Richard was seeking the hand of Princess Joanna of Portugal after Anne's death.
I like the Marie and Maximilian idea.
True, Joanna also brings more benefits to Richard than Marie, the latter of whom can only offer Henry Tudor's head if he still winds up in France. Marie and Maximilian is more likely and benefits both sides (Maximilian can guarantee his son's lands will be safe and Louis can get the Habsburgs off his back).
So a bit like Henry V/Catherine of Valois? And then we remember what happened from THAT union...