It actually was 1849. But I like the idea of Friedrich Wilhelm just refusing the offer instead of the usual PODs we get with the War of German Unification going the other way, or Russia not stepping in to broker the timely armistice.
Probably Franz Joseph could have crushed the German Parliament, but there are investing ramifications.
Does the new Prussian constitution go away too? Because if it does, things do quiet down a lot. If the Prussian constitution stays in place, Friedrich Wilhelm or his brother Wilhelm may have to call Bismarck in a Chancellor like they did IOTL to handle the Reichstag. And even if Bismarck is just in charge of Prussia, things get very interesting, though I think in 1848-50 he was not that favorable towards German unification.
With the Hapsburgs having recovered their footing, do they avoid the Triple Monarchy? It was only due to the defeat by Prussia that they created the Kingdom of Italy, combining Lombardy and Venetia with Tuscany. And that precedent was important in the creation of the Kingdom of Hungary later on. The fact that they are still heavily involved in Germany, and they have not suffered that big a loss of prestige, may persuade them against it.
And then you have Napoleon III which is a huge wildcard. Yes, IOTL he stuck closely with his alliance with the British and concentrated on boosting his prestige with colonial ventures. But with Germany right on his borders he had to be cautious. Who knows what he would have tried otherwise. And there would have been no need of the OTL alliance of the French Empire with what became known as Austria-Italy.
The pattern of liberalism and nationalism being mostly defeated in 1848-50, then governments making concessions anyway at a slow pace, still happens, but in terms of diplomacy and balance of power, a united German makes a big difference.