I noticed that The UI is being upgraded from gtk+ to gtkmm I would like to try and get Pen Tablet support (it is probably a good time). My early experiments in doing this are not doing too well (considering that the GTK documentation is totally out of date).
That would be cool. However getting extended events from gtk(mm) is probably the easiest part. Much more difficult is to decide what to do with the pressure data. Of course it's natural to try to adapt the calligraphic pen to use it for variable stroke width, but I would not recommend it because that tool is very limited. It creates plain SVG paths, instead of separate axis path and stroke width information that would allow to edit a variable-width stroke as a regular stroke while preserving its width information. See this post:
http://sourceforge.net/mailarchive/message.php?msg_id=8193379
That said, if you just hook up pressure sensitivity to Inkscape that would be very useful by itself. It may have other uses outisde variable-width strokes.