Okay now your question is more clear to me(or maybe I now read it properly).
Integrating the Mark-X in to the market like the US for example would add a car which is the same as the IS350.
Now, that would be a mistake(in my mind at least) as the market would have to choose between two different cars that are almost identical and from the same manufacturer.My guess is that would decrease the sales of one specific model, and certainly any company does not want decreased sales.
Car companies generally introduce cars to fill a gap in a specific segment/class of vehicle, right now I don't see a place for the Mark-X OR A luxury RWD sedan.
Coming to the second part of your question about the features added.I can't fully answer that but I assume features in cars depend on the market.
Take the example of Pakistan: Most of the people care about the resale of a car rather than the safety features offered, that is the reason why you see the crap build quality and safety features of cars offered in Pakistan.
Now you might know that older BMW's did not have cup holders(I have read this somewhere,can't recall), but due to the US market they had to cater to the requirements of the people and implemented them.
Features offered depend on the competition and the demand of the people.
I hope I answered(to some extent) your question