Key interlocking ("Schlüsselwerk" in german) would be quite tricky to implement as it will require quite a lot of interactions with the in-game infrastructure and some way to pick up objects.
Electromechanical interlocking would be relatively easy, as it could either be implemented like the mechanical interlocking or via a seperate program using the same interface the SPK/SCS/SCE already use.
For gameplay purposes, a generic S&H 1912 simulation with maybe some slightly different user interface looks (mechanical indicators/lamps for points detection) should suffice as most of the differences between the various variations are behind the scenes and at least some of them are german specialities. Yet, I'd also suggest the VES multi-row frames which use the same technology but with a far more compact user interface.