It was, should the Austrians have won the Austro-Prussian War it is rather likely that they would reacquired Silesia from the Prussians.
I disagree. After all, let's look at how the war started, what it was hence about besides the general Austro-Prussian dualism in Germany and what hence the war aims were:
1) The future of the German Confederation. That is the big one.
2) The status of Schleswig, Holstein and Lauenburg, between 1864 and 1866 jointly occupied by Prussia and Austria
3) If both those are settled, then maybe one can talk about territorial adjustments, reparations, etc.
First of all, Austria will push for a) restoration of the German Confederation and b) a reform of the German Confederation according to its wishes - something that will give it more effective dominance within it, and something that will enable Austria to have some guarantees Prussia won't pull the same trick again.
Second of all, Austria will insist that Schleswig-Holstein be made an independent duchy under the House of Schleswig-Holstein-Augustenburg. The dispute about this is what ultimately triggered the war, after all.
Only once those aims are fulfilled will Austria turn to territorial questions. But the thing is, for Prussia to submit to such terms and also cede land - for that to happen you don't just need a victory against Prussia, you need a decisive and crushing victory. Basically, for Austria to be in a position to demand Silesia back, everything in the war would have to go right for them.
And then, and then, there is yet another problem: Napoleon III. The thing is, IOTL, all his plans for Germany were foiled when, against expectations, Prussia won the war. His plan had been for Austria to win and make demands against Prussia, and then for him to appear as saviour as Prussia - against concessions for France in the Rhineland, of course, maybe even the re-establishment of the Rhine border. This plan was crushed when Prussia won IOTL, and then Bismarck's quick peace with Austria (done quickly for exactly that reason) robbed France the chance to find another reason for an intervention. But ITTL, things go exactly like expected by Napoleon III, so chances are he will in fact try to intervene now, which will cause quite some chaos.
Firstly, I don't think they will avoid the Dual Monarchy. It might be postponed, both by the added number of Germans and because Franz Josef II and his advisors are going to be a lot more confident about their own position. Nonetheless, the Dualism Act will still be passed eventually, the Hungarian population is still too large and too 'uppity' for such a compromise to be put off forever, even with the acquisition of Silesia in 1866.
I disagree. The Ausgleich came about because it was widely perceived that Francis Joseph's attempts at neo-absolutism had failed, but that perception largely came about because of the disastrous war of 1866, where Austria was pushed out of Germany and also lost Venetia. Without that loss, there won't be any pressure for change for now. And even if such pressure mounts, the Ausgleich is by far not the only solution. The Czechs are getting restless as well, and if the Ausgleich is delayed, then by the time something happens might already be an problem as well - a problem obviously not solved by an Ausgleich with just Hungary. In fact, that will only incentivize them to be even more restless in the hopes of getting the same deal, which is what happened IOTL at first. What happened IOTL is basically that Austria made peace with the second largest nationality in the realm, at the price of throwing the other nationalities in Hungary under the bus, and creating a huge power bloc east of the Leithe that would be a problem again and again and again and make demands again and again and again.
It was, frankly, not a very intelligent solution, and mostly came about in the historical form due to the influence of the magyarophile Empress Elizabeth and the need for a quick "do something!" solution. An imperial reform towards genuine federalization, or maybe just strengthening national minorities within Hungary in order to weaken the Magyars, is very well on the table as well. In 1848, when Hungary rebelled but Habsburg still held Slovakia and Croatia and the Hungarians were fighting in Transylvania (because of course the Hungarians spent the majority of their 'War for Independence' actually busy repressing the other nationalities in their kingdom) there was the seriously considered proposal that the Emperor should take on the title of a "Grand Prince/Grand Duke (
Großfürst) of the Romanians, Slovakians and Ruthenians". Such ideas might be used again. A more stable Austria that isn't seen as on the way to political failure might not make a, frankly, overly hasty compromise with the biggest nationality and then leave it at that.
Well, following the Hapsburg penchant for retaining traditional bounderies they'd be obligated to re-attach Silesia to the Crown of St. Wenceslas, which would give sufficient strength to a Bohemia-Moravian "Kingdom" within the Monarchy, I could easily see Vienna pose to the Magyar gentry that if Hungary gets privileges, legally they'd be obliged to give it to Bohemia and Croatia as well, which puts them in a better negotiating position.
There was no Bohemian-Moravian Kingdom within the monarchy. Bohemia, Moravia and (Austrian Remnant) Silesia were separate crown lands. If Prussian Silesia is annexed, which I still find to be a pretty big if, than it will get reunited with Austrian Silesia, and you'd still just have a crown land of Silesia, just one that is multiple times bigger now.
I'd expect Gerrymandering to produce disproportionate German governing power
In those days it wasn't done by gerrymandering, but by census-based franchise. Basically, only a fraction of the people held the franchise at all, based on taxes paid, and of those people, different classes of tax payers often got differently weighted votes. And since the Germans usually were wealthier than the surrounding Slavic population, and since the old nobility was usually more German than Slavic as well (usually - there were of course also many proud Czech nobles in Bohemia) that usually gave German populations (but in the south also Italian populations) disproportionate representation, usually to the point that as a minority that had a majority in parliament (Germans in Bohemia and in Moravia, Italians in Dalmatia), at least until the election reforms that swept Austria in the 1890s and 1900s.