To show missing values as NA, it would be nice if we could do the following. It's easy to workaround this, but given that NA is common in other packages this would be a useful addition.
options missing='NA';
data class;
set sashelp.class;
if age=12 then call missing(age, weight);
if age=13 then call missing(height);
run;
proc print data=class;
run;