Just to clear up a few matters ...
This set has never died; it only went to sleep. Because there are many other projects I currently work on, that take my time. Everything is only a matter of having enough time, and this set together with the Swiss Set had to give way to all those other projects. Once those major projects are nearing completion, then this set may just as well be resurrected.
... Concept ...
there has always been a concept, but it was never publicized, for obvious reasons (and I'm not going to mention them).
But, here is a summary :
. there are plans for a base set, that allows to play an entire game but with enough free vehicle ID's for one of several expansion sets. Each of these expansion sets have a strong theme, and they are :
a) passenger only transport, pre-1950.
b) passenger only transport, 1950-present day (before all rolling stock went all red).
c) international passenger only transport, including all European trains from neighbouring countries visiting or transiting Germany.
d) freight only transport.
e) futuristic trains, like the TransRapid and its many versions.
. once complete this set and its sub-sets would have little to do with any other set currently knowm. Surely, there are players out there, who would welcome such variety. These sets would reach into other parts of Europe with international passenger trains, and also include 'East Germany' as it was known in the past.