I'm gonna violate my own continuity here and give my readers the choice of which scenario they would prefer.
P.S. I've been toying with this scenario for a while, but rather than create a completely separate timeline, I decided to work it in here.
Let me know via PM which you'd prefer.
1647 - Vienna is en fête, the elder surviving daughter of Ferdinand III and his recently deceased Spanish wife, Maria Anna, has been in negotiations to strengthen the bonds between the Habsburgs in Spain and the Imperial House. All that remains is for the dispensation to come from Rome regarding the marriage (Maria Anna and Baltasar Carlos are first cousins, after all). And once the Emperor has pulled off that marriage, he sees no reason why he should further delay the marriage of his older surviving son, also named Ferdinand (who was crowned king of Bohemia the previous year) who stands to be crowned king of Hungary later in the year.
Ferdinand III is casting his eye towards D. Felipe IV's daughter, Maria Teresa to marry his elder son. Of course, there is news on other fronts, too. Namely that the cousin of the French king, that fabulously wealthy heiress, Anne Marie Louise d'Orléans, duchesse de Montpensier, and widow of the Cardinal-Infante Fernando, Governor of the Spanish Netherlands, is tossing her hat into the ring to be the new empress. Her only pregnancy by the infante resulted in a daughter - the Infanta Maria Luisa Margarita. After the Infante's untimely death (when the rumors had been flying that he had planned to declare himself as independent ruler of the Netherlands) the widowed Madame-Infante has been living in Brussels with her daughter - who much like herself, will be the greatest heiress of the age when she grows up. The reason? This currently 6-year-old infanta is in line for the Spanish throne, and due to the marriage contract stipulating that no son issuing from the duchesse's marriage could inherit her properties in France, any man who marries her will pass the five duchies, and numerous other French properties of Madame-Infante to his son. This of course, is assuming that Madame-Infante produces no sons by another husband.
Of course, at the same time that Madame-Infante is offering herself for the position of Empress-Consort, she's also offering her daughter to her former sister-in-law (and aunt), the French regent, Queen Anne, to marry the currently 9-year-old Louis XIV.
On the other hand, Henriette Marie, Queen of England (who just happens to be another of Madame-Infante's aunts, as sister of the late king) is eyeing the widowed governess of the Netherlands as a match for the prince of Wales. With the young lady's fortune, they could finance enough troops to help fight the war going on over the Channel. And as a double insurance policy way of making sure that at least part of the fortune still ends up in Stuart hands if the lady is unwilling (as she's rumored to be), a match between the prince of Wales and the little infanta is also booted around. However,several members of the queen's court-in-exile point out that such a match would hardly be fortuitous, despite the amount of gold Madame-Infante could bring. England has turned rather anti-French as well as anti-Catholic as a result of the queen's wheeling and dealing. Also, those with longer memories can still smell the fires of Smithfield where the heretics were burned by the Catholic Queen Mary I and her Spanish husband - which is theoretically what Maria Luisa would be seen as: a Spaniard. So, for all their coin, Madame-Infante or her daughtermight be the nail in the coffin of the monarchy in those Isles.