[NTG-context] two features in ViewerPreferences for printing

Hans, for a small book I’m publishing online (https://archive.org/download/ensayo-escritura/ensayo-escritura.pdf), it would be extremely useful to have two features from the PDF spec implemented. These are PrintScaling and Duplex (page 364 of the PDF spec). They are two entries in the ViewerPreferences. Both features are extremely useful to avoid issues when explaining double-sided printing and not reducing margins (in some cases, this reduction to margins is critical [such as in the sample above]). I think this is not only useful to many users. Could these features be implemented in ConTeXt? Many thanks for your help, Pablo -- http://www.ousia.tk