I'm dropping the list an email because I wanted to make use of the C++ Contourable_Data class to plot contours. Currently only the plstream::shade member function seems to permit use of the Contourable_Data class and not cont and shades. 
I was considering writing my own implimentation of these members and submitting them as a patch, but I thought that there is at least one design descision to be made in terms of how the contour/colour levels should be passed, eg a PLFLT* and PLINT giving the levels and number of levels, or another more object oriented way with bounds checking or something.
Perhaps also there is a previous discussion and reason why these haven't been implimented that I'm not aware of.
I will probably write my own version of these interfaces anyway so if it can be done in a way that everyone else is happy with then I'm happy to do it that way and send patches.