So I've been thinking this over a bit more and I was wondering about the plausibility of the Sobieski marriage. I'm thinking specifically if we back date Max Emanuel's death to the Siege of Belgrade (Sept 6 1688). Let me know if this makes any sense.
So to start I think the Imperial army still takes Belgrade, Max Emanuel just dies from his injuries. As that was basically the end of the campaign for that season not much else changes immediately. So the Austrians are left in control of most of the right bank of the Sava and the Danube as far as Smerderevo below Belgrade. Definitely poised for a big campaign next year as they did OTL yet their commander has just died, which may affect moral but more importantly the loyalty of the new Elector of Bavaria isn't necessarily assured and trouble is brewing in the West.
The geopolitical situation in Germany is tricky. With Max Emanuel dead his brother Joseph Clement automatically becomes Elector of Bavaria, but Joseph Clement was only a month before named Prince Archbishop and Elector of Cologne by the Pope after a contested election. So he will have to surrender the Ecclesiastical Electorate. This puts the Emperor in a bind as the French backed William Egon von Furstenberg is currently fighting for control there. The Bavarians had always flirted with a French alliance and the French ambassador in Lisbon and Joseph's sister, the Dauphine, had just a couple years earlier been back channeling a match between him and the Infanta Isabel Luisa da Braganza. So I can see the French working even harder to try to detach the new Bavarian Elector from the Austrian camp and to get him to surrender his claims to Cologne to von Furstenberg. I'm not sure if Leopold would be inclined to offer Joseph Clement his brother's widow or if that's even really plausible even with the Pope on board but absent that he doesn't have any major carrots to entire the new Elector. Also this is not to say that Jospeh is automatically inclined to switch sides but for Leopold it has to be a major concern.
IOTL Louis would invade Germany in September so the pressure's on. The logical successor as an Imperial candidate would probably be Ludwig Anton of Pfalz-Neuburg since he was a canon at Cologne and helped orchestrate Joseph Clement's sort-of-election. But he will have an uphill battle even if the Pope gives his blessing (which he probably will). So Leopold needs to keep Joseph Clement on his side not just to secure Cologne but also to keep Bavarian troops in the field lest the new Elector recall them. OTL the Austrians would have to withdraw forces pretty soon, and after massive success in 1689 in which they briefly reached as far as Skopje all their gains beyond the Danube would be lost by the end of 1690. Now, of course, they wouldn't know that at the time but Leopold will certainly feel pressed in the West with the French invading Germany, the Imperial candidate in Cologne having to abdicate and the new Elector of Bavaria potentially being unreliable. In the east they've taken Belgrade but it wasn't easy and they may have to pull back troops to send west allowing the Ottomans to regroup. The Ottomans would crush the Chiprovtsi Uprising in NW Bulgaria in the fall of 1688 so they've just demonstrated that they're still capable of retaliating even after loosing Belgrade.
So into this situation the marriage of Maria Antonia comes up. I think John III would certainly put forward his son again. Leopold had once promised her to James Louis before the Siege of Vienna so when's he's desperate enough he's willing to put aside his pride and ego. I'm certainly not going to make out that the situation in 1688-89 is as bad as in 1683 because of course it's not. But it's not great either. On the other hand, after Vienna John III was riding high, hailed as the savior of Christendom with designs on Wallachia, Moldavia, maybe even Transylvania. Leopold certainly wasn't going to stomach marrying his then only daughter to his rival's heir. But flash forward to 1688 and John's position has deteriorated. His two campaigns into Moldavia have both ended in failure, he's failed to retake Kamianets from the Turks and he's been forced to make a disadvantageous peace with the Russians to get them on side. So he's less of a rival now. In 1690 when the Austrian's had to pull out troops from the Balkans they were willing to discuss coordination with Sobieski and agreed to a deal that allotted him Moldavia and the Austrians Wallachia. So a deal could be had.
So what I'm thinking is that a deal is reached and sealed by marriage. Leopold agrees to marry Maria Antonia to James Louis. They are given a Duchy in Silesia, maybe Opole or maybe his OTL Duchy of Olawa. I could see Leopold insisting that Maria Antonia is made Duchess in her own right so that she can hold it if Jakub dies and he doesn't get to keep it if she dies first without kids. Anyways it gives Jakub some territory outside Poland which John III really wanted so that somewhat alleviates the need for another Moldavian campaign. OTL he convinced the Sejm that the strategy was to invade and conquer Moldavia to cut of Kamianets from Turkish supply lines. They were less than impressed with the results. So here the new strategy could be to move against Kamianets directly or at least make some incursions there to tie down the Tatars while Jakub leads a Polish contingent to join the Austrians and invade through Serbia into Bulgaria and Thrace and deliver a knock out blow to compel the Ottomans to make peace. I'm not saying it would work but on paper I think its a convincing strategy.
So both sides get something. Leopold gets troops to reinforce him in the Balkans so he can divert troops to Germany to counter the threat there. He keeps Poland squarely on his side in the looming War with France, Maria Antonia renounces her rights to Spain and is compensated by being made Duchess of Opole. She marries a Polish Prince who couldn't realistically pose much of a threat to Leopold in Spain or Spanish Italy (I know, I know, Spain may still name their child heir but from Leopold's perspective a Sobieski seems less likely to want to or even be able to go to Spain than a German prince), John gets some territory for his son and prestige from the marriage, they're able to make a coordinated assault on the Ottomans.
So is this realistic? Obviously it's not a slam dunk but I think it's a plausible scenario.