(sorry to write in English...)
From the point of view of an English person living in Germany, I don't see that left or right hand drive makes any difference to producing these special editions as the modifications are mainly only to components shared between the UK and German cars!
The main difference is firstly that Germans don't want to by Impreza Turbos. In the UK, they can easily sell 500 limited edition STi's, In Germany they struggle to sell 500 standard STi's in a year, so what chance have they got of selling enough limited edition models to make it worth while! You only have to compare Scoobynet to this website to see the diffence in the number of people interested in Suabru's!
The other big problem is TÜV. In the UK they can get away with more leanient regulations for emissions and noise using the Single Vehicle Approval (SVA) regulations. They can't do this in Germany so easily. The STi is already close to the limit regarding TÜV regulations, so to get anything "Special" approved would be near impossible. For example, its even impossible to get the Prodrive PPP in Germany!