Coming in late to the discussion, but I'll try my best to give my ideas. Ultimately, one of the core problems of Germany's toolkit right now is how anachronic it is (Hanse from HRE, Realpolitik from Bismarck, Panzer from Third Reich), with the additional problem of "Realpolitik" not quite reflecting how Bismarck established his foreign policy. Lastly, Germany's toolkit is very one-dimensional, which makes it quite boring from a gameplay perspective.
While I quite like Pineappledan's Blood and Iron proposal from a gameplay perspective, this vision of German diplomacy would represent more what Prussia (before unification) or Germany (under Wilhelm II, who dismissed Bismarck right away) would do - something reminiscent of "Gunboat Diplomacy", which is already an Autocracy trait.
Bismarck as Chancellor of Wilhelm I was ultimately a master of maintaining peace within Europe, despite building his reputation in times of war and his "Blood and Iron" speech as Pineappledan pointed out earlier in this thread (note: this speech was uttered before the German unification in 1871). He was also disinterested in building German power away from Europe, being pressured into colonialism by other parties within the German Empire. I believe that thematically this would call for a proximity-based diplomatic civilization, with heavy focus on maintaining peace with your surroundings. Now, in Civ 5 CPB and especially in higher levels of difficulty, one of the main concerns of diplomatic civs (which pretty much every one agrees Germany should stay) is to maintain their relations with City-States and trade with major civilizations without causing wars/discontent over city-state influence - which is why I propose the idea of Germany being the only civ that gains diplomatic power without being actually allied with city-states themselves.
Economy-wise, Bismarck was heavily protectionist as displayed by his tariffs on foreign exports such as Russian grain. His "reign" was also the period where German cartels were created, such as the Steel cartel, which would argue for a mercantile economic approach, much opposed to what the Hanse currently offers.
Lastly, as pointed earlier in the thread, Germany was one of the industrial and scientific leaders of the time, with many of the world's most prominent scientists and engineers at the time being German. I believe this should be reflected in Germany's toolkit.
UA: Realpolitik
City-states you have a Trade Route with grant you ally benefits and cannot declare war on you. When you broker peace between two other major civilizations, gain 1 extra Trade Route slot.
UB: Industrial Confederation
Replaces the Workshop.
Shares its common traits.
+1 Great Engineer and Great Scientist points in the Capital, scaling with Era.
+2% production and gold in the city for every Internal Trade Route.
UU: ??
I'm a bit short of ideas on this one, as long as it is not anachronic (e.g., Panzer)
Overall, this version of Germany would give the player and AI significant flexibility with trade route usage: either to gain diplomatic benefits without the downsides of increasing tensions with other civilizations, or to power the German Industry. It also makes Germany the only civilization in the game that actually benefits from peace (as opposed to the Aztec).
It also powers up Germany's generation of Great Scientists and Great Engineers, a feature I believe would be far more thematic than converting 10% of gold to science every turn (like the Hanse currently does).
I am not informed enough on how the German military worked at the time so I'll leave this to you guys.