The translated article quotes Mr. Multhaupt, as saying that the engineers and designers take steps to insure that these variants will be possible with limited modifications. The one factor that leads to broader offerings is consumer demand, which Mercedes hasn't seen, yet.
We're not sure about the diesel, but it's probably a no-brainer that a droptop version of the S-Class based coupe will make it to production. Soon.
[Source: Auto Motor Und Sport]