I agree with the possibility of multiple "Germanys", even with a POD as late as say the Austro-Prussian War. United Germany is not an inevitability. I am sure man Pan-Scandinavians felt that such a union was a guarantee of the historical dialectic as much as the Pan-Germanics did.
If Bismark's gamble fails, the German Confederation would be in tatters, Prussia is disgraced and, honestly, Austria is no longer in a position to be the dominant leader of the German states, what with their extensive non-German holdings, although they could still be very influential.
What is required is a stable condition to develop between several smaller German states, a consolidation of the messy Kleinstaaterei, which results in the reforming of nationalist zeal away from "Pan-Germanism" into Saxon Nationalism, etc. If the entrenched conservative powers can successfully develop these new national identities, while successfully limiting influence from the other kingdoms/realms, then 'Germany' can develop without political union.
I always imagine a POD that involves France getting involved against Prussian intervention, perhaps the Hanoverian Army successfully uniting with their southern allies combined with an alt-Königgrätz allows a window for France to move. The war is more damaging to Germany and the ability of the smaller powers proves impotent in the light of modern, industrial warfare. The Great Powers, as was custom, negotiate for a restructuring. France, Austria, UK and Russia are all involved.
I personally enjoy consolidation into several Kingdoms, with a second German Mediatisation occurring. We see the German region split into several camps and Prussia is silenced before it causes more problems.
Aligned with Austria, Saxony reclaims Prussian Saxony and the minor powers of the Saxon region. Baden is elevated into a Kingdom and a "Southern German Confederation" (yes a cliche) is formed with Württemberg and Bavaria. Saxony is firmly in Austria's camp but the SGC is more independent, wavering between France, Austria and their own causes.
France's involvement sees the elevation of West Prussia, Hesse and and the Rhine provinces reconstituted as the Kingdom of Westfalen. The UK is satisfied because a Prince with sufficient British ties (there are several to choose from but I welcome suggestions) is elevated. Luxembourg's fate is up for discussion. Although supposedly a satellite of France's, Westfalen will inevitably exert independence, being such a potent industrial power. Westfalen the the SGC are natural allies, eventual forming their own block against Austrian and French influences.
The Kingdom of Hanover remains and gains Oldenburg and Holstein, while Schleswig is returned to Denmark. The fate of the Mecklenburgs hangs in the balance, but I prefer seeing them consolidated into Hanover as punishment for siding with Prussia. Hanover is viewed as a third Low Country, in a geopolitical sense, and Great Britain is satisfied having friendly states lining the North Sea.
The Prussian Question remains. Their only friend in the world is Russia, and castrated as they are by the removal of the Rhineland, is more of a satellite than ally now. Austria will most likely demand and receive Silesia, but it could possibly be divided between Austria and Saxony, maybe Russia getting a slice.
Bismark and, probably under pressure for allowing such scheming, Wilhelm I are both forced out of power. Ideally, the Junkers are shamed, Frederick III rules from 1866 - 1888 (longer depending on butterflies, such as getting kicked off his horse during the war and lands hard on his back, giving up smoking due to the injury to his wind) bringing in many reforms, and flipping from Russia's authoritarian sphere to the UK's. Maybe, if we really want a reform-wank, Prince Wilhelm succumbs to childhood illness and we see a King Henry.
The situation is tense but stable. None of the remaining Germanies have the ability to unite with the others. Each is stable enough to develop and nurture their separate identities. Economic spheres and unions may develop but the once potent Pan-Germanism that fed the revolutionary flames of 1848 has been extinguished by the blood spilled in 1866-1867.
.... just my two cents.