Monsieur Gaston will ascend the French throne.He's the current French heir and hates Richelieu's guts. Also, we just happen to have a bunch of Huguenot assassins running around. Perhaps they will make an attempt on Richelieu, and get King Louis instead. Richelieu, of course, will promptly get the hell out of Dodge. Defecting to the USE would be too obvious, but he could go elsewhere, possibly joining the Dutch Hapsburgs, or even try to carve out an empire of his own in the New World.
If Gaston becomes King of France, he will become a popular meme amongst the Up-Timers.
The Spanish colonies in the New World will break away far earlier than they did in our timelineThe USE is soon to deploy a new blue-water fleet that, while still composed of sailing ships, will be far more powerful than the current ships of the Spanish and French navies, and there would be plenty of good reason to use those ships for commerce raiding. So there is an opportunity for some ambitious governor to pull a Sepoy Option, and establish a new sovereign nation in the New World.
In the next book taking place in Italy, Borja will learn exactly how the future remembers the organization he leads.Come on. The fact that they've had two books so far with the head of the Spanish Inquisition as Big Bad, without any uptimer making a single Monty Python reference indicates superhuman control on the part of the authors. Sooner or later it's got to happen.
Murad the Mad will become the new Big BadFirst, his invasion of Austria will succeed, bringing the Ottomans into direct contact with the USE. Then, Murad will do the smart thing and go after Italy. The USE won't intervene at first, since he'll just be fighting their Spanish enemies, but if Murad can take Rome (and if the Portuguese and Catalan rebellions go off), he'll quickly become a clear and present danger.
There's one person who won't be butterflied away.You may remember that Gustav gave Julie Sims a barony in Lappland as a wedding present. It's not inconceivable that she might retire there. And eventually, her line will produce Simo Häyhä.
The cover-ups of Huguenot crimes will be discovered.There may be hell to pay when it is discovered that Mike Stearn's and some of his Jewish advisers used several acts of terrorism by Protestants to punish anti-semites. Considering the important figures later murdered by the Huguenots in their attempt to start a war, it may well be seen by some as sacrificing the safety of Calvinists, Lutherans, and Catholics in favor of Jews, witches, and the French. Of course anyone who found this out and tried to tell others might not be believed or ends up being murdered.
The USE boxing championship will be named after Hans Metzger.He was adored by the spectators, respected by the other boxers, and died undefeated when he was murdered for refusing to cooperate with people trying to rig a match - and killed or maimed every single one of the people sent to murder him before he went down. The combination of skill, sportsmanship and integrity he showed will be held up as the example of what a champion boxer should be.