For other banks.
Sparkassen customers dont need to pay at other sparkassen belonging to the same group (I think it depends on how the different regions organized themselves)
They can also do coorperations between other banks like for ing-diba and other institutes.
They are already interconnect at various points.
Schools are connected to university networks, university networks to loval government intranets and those are again probably at some point connected to the federal network.
I don’t wanna guess where else they have connections to like the police or legislative network.