Hi,
A while ago I asked the Inkscape list whether there was interest in an implementation of my curve sketching algorithm (see the thread at http://sourceforge.net/mailarchive/message.php?msg_id=24902605). There seemed to be interest and I wrote a cleaner (and much faster) version, although this took longer than I anticipated. There are still a bunch of improvements possible, but at this point it's quite usable. The code and a windows installer for a demo binary are available at http://code.google.com/p/cornucopia-lib/ and there's some documentation.
I am completely unfamiliar with Inkscape's codebase, so the integration would need to be done by one of the Inkscape devs. As a proof-of-concept, however, I wrote a very crude replacement of the bezier_fit_cubic_r call with a call to Cornucopia in the pencil tool (patch attached--of course, you have to build and link to Cornucopia to try it). For the real thing, I'd need to find a better mapping from the "smoothness" slider in Inkscape to my myriad of parameters.
Is someone interested in working on this? I would, of course, help in what way I can (although I'm pretty busy these days and my response latency may be high occasionally).
Thanks,
-Ilya