I already create a Flow-Chart plugin for TWiki, and that
draws a SVG in the web server before to make the PNG
to send for the web browser:
http://twiki.org/cgi-bin/view/Plugins/FlowchartPlugin
That may be a start...
I like the idea of an Chart collection plugins, but it may
need a complex input interface, and may be useful to
create the interface with PyGTK instead an Inkscape
extension interface. There are a problem in PyGTK
extra dependence? Will be a problem for Windows
users? If yes, the inkscape win package may provide
that lib?